Fix processing in SAX2 in case of an allocation failure

Related to https://bugzilla.gnome.org/show_bug.cgi?id=731360
Avoid Possible Null Pointer in trio.c

For https://bugzilla.gnome.org/show_bug.cgi?id=730005
While using assert in libxml2 is really not a good idea, it's
still better to assert than crash
Check for tmon in _xmlSchemaDateAdd() is incorrect

For https://bugzilla.gnome.org/show_bug.cgi?id=732705
In _xmlSchemaDateAdd(), the check for |tmon| should be the following
since MAX_DAYINMONTH() expects a month in the range [1,12]:

    if (tmon < 1)
	tmon = 1;

Regression introduced in
https://git.gnome.org/browse/libxml2/commit/?id=14b5643947845df089376106517c4f7ba061e4b0
Fix building when configuring without xpath and xptr

For https://bugzilla.gnome.org/show_bug.cgi?id=732735
schematron little used code and xptr rely on XPath, fix the
configure script.
Merge branch 'master' of git://git.gnome.org/libxml2 into os400