[phobos] std.process

[Brad Roberts]

Lars has been trying to land a major overhaul to std.process for a long time
which has been blocked by some issues for which patches have been available for
a long time:

Walter, can you please incorporate the patches in bugs:
  190 -- patch applied, caused regression bug 4753 so was reverted.
  4753 -- fix for the bug caused by 190's fix was added
  3979 -- probably should be closed as a dup of 190, but is the bug Lars filed

I've updated and merged the changes into a new attachment on bug 190.  I've also
run all the test suites for a 32 bit build on linux.

Thanks,
Brad