reconsideration of header files

[davidl]

The support of generating header is limited.

dmd -H -o- abc.d
still emits error messages, i.e., semantic checks still run, I didn't work  
out a way of bypassing the semantic check by commandline.


Then, I assume header files only for interfacing, it helps a little for  
boosting up compile speed. Only way of siginificantly boost the  
compilation speed is feeding dmd everything at one time. An obvious  
example is compiling dwt , almost every files need 3 sec to be converted  
as an obj. By the way, rebuild 0.78 seems always compile one at a time, it  
seems that is related to dmd module system change.

I'm just curious where the time goes. 3 sec for compiling 1 file to obj is  
almost unbearable limit for most developers. I've already converted all  
dwt .d files to .di files by utilyzing the dmd -H option. There seems to  
be some other time consuming stuffs.

D header files are never used widely in projects. Maybe we should discuss  
it a little bit further.