Fixed MGTwitterLibXMLParser #include <libxml/xmlreader.h> not found compilation error on Xcode 5 with OS X Mavericks

http://stackoverflow.com/questions/6592193/how-to-solve-libxml-xmlreader-h-not-found-error-in-twitter-integration-in-ipho
Merge pull request #1 from jamztang/master

Fixed MGTwitterLibXMLParser #include <libxml/xmlreader.h> not found comp...