Remove trailing whitespace in Makefiles.
Build system cleanup and improvement.

* Split out PG_CFLAGS and GLIB_CFLAGS so they're only calculated once.
* Rename all CFLAGS_* variables to *_CFLAGS.
* Split compile and link into CFLAGS and LDFLAGS respectively.
Makefile.conf : Restore COV_CFLAGS which got lost in cleanup.
Merge pull request #11 from erikd/master

Build system cleanup and improvements.