fix this; the previous code gave the wrong md5sum when called in certain

fix this; the previous code gave the wrong md5sum when called in certain

	* glib/gchecksum.c (md5_sum_update): fix this; the previous code
	gave the wrong md5sum when called in certain ways with buffers
	larger than 64 bytes.
	(g_checksum_update): remove the unnecessary "length > 1"
	restriction

	* tests/checksum-test.c: Rewrite this to be much more exhaustive
	(and in particular to test the md5_sum_update bugfix).

svn path=/trunk/; revision=6314