Micro-optimize XML calls

*Summary*:
First Commit: Don't global variables that aren't actually used at all.
Second Commit: If debug is not enabled, don't even put it in the call stack.  This removes the debug() check on production path, but lets you still enable it with ?debug=1 (as you would before)
Third Commit: Only global a variable if we truly need it.  The less variables we look up, the faster it is.

Overall, these changes saved about 10% on page loading time against 26mb of XML.  (If I remember correctly anyways.  I wrote this a while back.)

I apologize for the first commit being a merge - my gitfu is weak.