INCLUDES is the right way to add to CFLAGS, not DEFS. Also there are bugs

INCLUDES is the right way to add to CFLAGS, not DEFS. Also there are bugs

	INCLUDES is the right way to add to CFLAGS, not DEFS.
	Also there are bugs with '+=' in makefiles.

	Got rid of DEFS line by moving G_LOG_DOMAIN setting into INCLUDES.
	Removed redundant -I from INCLUDES.

	This fixes an annoying bug where autoconf's DEFS, which includes
	the important -DHAVE_CONFIG_H, was lost.  (due to += weirdness)