Limiting config.h's #includes

[Paul Eggert]

In Bug#24506 I propose moving some #include directives from src/conf_post.h to 
the files that need the includes. I'm mentioning this on emacs-devel for any 
people who don't read the bugs list and who care about this sort of thing.

The idea is that <config.h> should limit itself to configuration items 
appropriate for all C files. This is something that has bugged me for a while 
about Emacs <config.h>, and the precipitating event for the proposed patch is 
the problems discussed in the recent "unexmacosx.c and limits.h problem" thread.

While we're on the topic, the name "conf_post.h" should use a hyphen not 
underscore ("conf-post.h") as per longstanding Emacs file name conventions. 
Although the patch proposed in Bug#24506 leaves the file name alone, I'd like to 
rename it after installing the patch.