[&1.5] Issue 2715:	Formatted XML is not displayed in the browser when viewing an XML file
[&1.5] Issue 2715:	Formatted XML is not displayed in the browser when viewing an XML file

Changes:
- Prevent duplicate stylesheet workaround if XML pretty print is running (based on XBL bindings)

http://code.google.com/p/fbug/source/detail?r=5945

firebug/tracing-console,firebug/tracing-console