#705267 - add additional defines checks for support "./configure --with-minimum"

 https://bugzilla.gnome.org/show_bug.cgi?id=705267
Fix a possible NULL dereference

https://bugzilla.gnome.org/show_bug.cgi?id=705400
In case of allocation error the pointer was dereferenced before the
test for a failure
Clear up a potential NULL dereference

https://bugzilla.gnome.org/show_bug.cgi?id=705399

if ctxt->node_seq.buffer is null then ctxt->node_seq.maximum ought
to be zero but it's better to clarify the check in the code directly.
Fix XPath '//' optimization with predicates

My attempt to optimize XPath expressions containing '//' caused a
regression reported in bug #695699. This commit disables the
optimization for expressions of the form '//foo[predicate]'.
Fix XPath expressions of the form '@ns:*'

Use namespace for match-all queries on the attribute axis.