Raising the bar on Phobos unittest coverage

[Walter Bright]

With the new -cov=nnn (not pulled yet) and -main, we can now add to the build 
process a minimum bar for unit test coverage.

The current state looks like this, the percentages are the current coverage 
amounts. It's not bad, but there's a lot of low hanging fruit ready for pull 
requests!

 From now on, I'd like such unittest coverage (and justification for low 
coverage) to be part of the minimum standard for all new phobos modules.

         $(DMD) -cov=83 -unittest -main -run std\stdio.d
         $(DMD) -cov=100 -unittest -main -run std\stdiobase.d
         $(DMD) -cov=95 -unittest -main -run std\string.d
         $(DMD) -cov=71 -unittest -main -run std\format.d
         $(DMD) -cov=83 -unittest -main -run std\file.d
         $(DMD) -cov=86 -unittest -main -run std\range.d
         $(DMD) -cov=95 -unittest -main -run std\array.d
         $(DMD) -cov=100 -unittest -main -run std\functional.d
         $(DMD) -cov=96 -unittest -main -run std\path.d
         $(DMD) -cov=41 -unittest -main -run std\outbuffer.d
         $(DMD) -cov=89 -unittest -main -run std\utf.d
         $(DMD) -cov=93 -unittest -main -run std\csv.d
         $(DMD) -cov=91 -unittest -main -run std\math.d
         $(DMD) -cov=95 -unittest -main -run std\complex.d
         $(DMD) -cov=70 -unittest -main -run std\numeric.d
         $(DMD) -cov=94 -unittest -main -run std\bigint.d
         $(DMD) -cov=100 -unittest -main -run std\metastrings.d
         $(DMD) -cov=95 -unittest -main -run std\bitmanip.d
         $(DMD) -cov=82 -unittest -main -run std\typecons.d
         $(DMD) -cov=44 -unittest -main -run std\uni.d
         $(DMD) -cov=91 -unittest -main -run std\base64.d
         $(DMD) -cov=99 -unittest -main -run std\md5.d
         $(DMD) -cov=0  -unittest -main -run std\ctype.d
         $(DMD) -cov=100 -unittest -main -run std\ascii.d
         $(DMD) -cov=0  -unittest -main -run std\demangle.d
         $(DMD) -cov=57 -unittest -main -run std\uri.d
         $(DMD) -cov=51 -unittest -main -run std\mmfile.d
         $(DMD) -cov=95 -unittest -main -run std\getopt.d
         $(DMD) -cov=92 -unittest -main -run std\signals.d
         $(DMD) -cov=100 -unittest -main -run std\typetuple.d
         $(DMD) -cov=85 -unittest -main -run std\traits.d
         $(DMD) -cov=62 -unittest -main -run std\encoding.d
         $(DMD) -cov=61 -unittest -main -run std\xml.d
         $(DMD) -cov=79 -unittest -main -run std\random.d
         $(DMD) -cov=92 -unittest -main -d -run std\exception.d
         $(DMD) -cov=73 -unittest -main -run std\concurrency.d
         $(DMD) -cov=95 -unittest -main -run std\datetime.d
         $(DMD) -cov=96 -unittest -main -run std\uuid.d
         $(DMD) -cov=100 -unittest -main -run std\digest\crc.d
         $(DMD) -cov=55 -unittest -main -run std\digest\sha.d
         $(DMD) -cov=100 -unittest -main -run std\digest\md.d
         $(DMD) -cov=100 -unittest -main -run std\digest\ripemd.d
         $(DMD) -cov=75 -unittest -main -run std\digest\digest.d
         $(DMD) -cov=95 -unittest -main -run std\algorithm.d
         $(DMD) -cov=83 -unittest -main -run std\variant.d
         $(DMD) -cov=0  -unittest -main -run std\syserror.d
         $(DMD) -cov=58 -unittest -main -run std\zlib.d
         $(DMD) -cov=54 -unittest -main -run std\stream.d
         $(DMD) -cov=53 -unittest -main -run std\socket.d
         $(DMD) -cov=0  -unittest -main -run std\socketstream.d
         $(DMD) -cov=88 -unittest -main -run std\container.d
         $(DMD) -cov=90 -unittest -main -d -run std\conv.d
         $(DMD) -cov=0  -unittest -main -run std\zip.d
         $(DMD) -cov=92 -unittest -main -run std\cstream.d
         $(DMD) -cov=77 -unittest -main -run std\regex.d
         $(DMD) -cov=92 -unittest -main -run std\json.d
         $(DMD) -cov=87 -unittest -main -run std\parallelism.d
         $(DMD) -cov=50 -unittest -main -run std\mathspecial.d
         $(DMD) -cov=71 -unittest -main -run std\process.d
         $(DMD) -cov=0  -unittest -main -run crc32.d
         $(DMD) -cov=70 -unittest -main -run std\net\isemail.d
         $(DMD) -cov=2  -unittest -main -run std\net\curl.d
         $(DMD) -cov=60 -unittest -main -run std\windows\registry.d
         $(DMD) -cov=55 -unittest -main -run std\internal\uni.d
         $(DMD) -cov=0  -unittest -main -run std\internal\uni_tab.d
         $(DMD) -cov=0  -unittest -main -run std\internal\digest\sha_SSSE3.d
         $(DMD) -cov=50 -unittest -main -run std\internal\math\biguintcore.d
         $(DMD) -cov=75 -unittest -main -run std\internal\math\biguintnoasm.d
#       $(DMD) -cov -unittest -main -run std\internal\math\biguintx86.d
         $(DMD) -cov=94 -unittest -main -run std\internal\math\gammafunction.d
         $(DMD) -cov=92 -unittest -main -run std\internal\math\errorfunction.d
         $(DMD) -cov=31 -unittest -main -run std\internal\windows\advapi32.d
         $(DMD) -cov=58 -unittest -main -run etc\c\zlib.d