Endian portability #defines in GLIB

[Manish Singh <yosh gimp org>]

This was a feature requested by someone on irc, and I think it's good idea.

Simply put:

#ifdef WORDS_BIGENDIAN
#define G_BIG_ENDIAN
#else
#define G_LITTLE_ENDIAN
#endif

in glib.h. WORDS_BIGENDIAN is derived from the built-in autoconf test.

Just a small, simple addition to enhance glib as a portability lib.

-Yosh