Fix and add const qualifiers
For https://bugzilla.gnome.org/show_bug.cgi?id=689483
It seems there are functions that do use the const qualifier for some of the
arguments, but it seems that there are a lot of functions that don't use it and
probably should.
So I created a patch against 2.9.0 that makes as much as possible const in
tree.h, and changed other files as needed.
There were a lot of cases like "const xmlNodePtr node". This doesn't actually
do anything, there the *pointer* is constant not the object it points to. So I
changed those to "const xmlNode *node".
I also removed some consts, mostly in the Copy functions, because those
functions can actually modify the doc or node they copy from
6 files changed
