There's no simple way to make the doc/examples tests handle different
configurations. But these tests aren't especially valuable, so remove
the result file checks.
* xmlschemas.c, xmlwriter.c, doc/examples/parse4.c,
doc/examples/io2.c: minor warning cleanup (no change to logic)
* xinclude: fixed return value for internal function
xmlXIncludeLoadFallback (now always 0 or -1)