Enable more tests on Windows; move sort_by tests

Use %%FAIL IGNORE MSG for error messages that differ on Windows, and
move the sort_by/group_by tests that fail qhen qsort() is not stable.

Now only tests/sorttest and tests/shtest are disabled on Windows.

tests/optionaltest

@@ -0,0 +1,5 @@
+#!/bin/sh
+
+. "${0%/*}/setup"
+
+$VALGRIND $Q $JQ -L "$mods" --run-tests $JQTESTDIR/optional.test