Fix regressions introduced by CVE-2014-0191 patch

A number of issues have been raised after the fix, and this patch
tries to correct all of them, though most were related to
postvalidation.
https://bugzilla.gnome.org/show_bug.cgi?id=730290
and other reports on list, off-list and on Red Hat bugzilla
Fixes for xmlInitParserCtxt

let's make sure that parser options are updated too when a corrsponding
global variable or other field of the context is set.
Merge branch 'master' of git://git.gnome.org/libxml2 into os400