addition of maplibxml2.c

[Kralidis,Tom [Burlington]]

Devs,
 
I've committed maplibxml2.[ch].  This file contains convenience functions to those using libxml2 support in MapServer (such as mapogcsos.c, mapowscommon.c, and Frank's forthcoming WCS 1.1 addition).
 
I've also opened up a ticket to deal with changing the USE_SOS_SERVER ifdef, since now libxml2 support will be required by more than just SOS:
 
http://trac.osgeo.org/mapserver/ticket/2416

Cheers
 
..Tom