Add missing const. (g_strsplit): Add g_return_val_if_fail for case of

Add missing const. (g_strsplit): Add g_return_val_if_fail for case of

	* glib/gstrfuncs.c: (g_ascii_strdown), (g_ascii_strup): Add
	missing const.
	(g_strsplit): Add g_return_val_if_fail for case of empty
	delimiter, which can result in an infinite loop otherwise.
	* glib/gstrfuncs.h: Add missing const.
	* tests/.cvsignore: Ignore a generated file.

	* tests/array-test.c:
	* tests/dirname-test.c:
	* tests/hash-test.c:
	* tests/list-test.c:
	* tests/node-test.c:
	* tests/relation-test.c:
	* tests/shell-test.c:
	* tests/slist-test.c:
	* tests/spawn-test.c:
	* tests/strfunc-test.c:
	* tests/string-test.c:
	* tests/testglib.c:
	* tests/tree-test.c:
	* tests/type-test.c:
	Add an #undef G_DISABLE_ASSERT so all tests will assert even if
	asserts are disabled inside glib itself.