New 'profileerror' log group for profiling errors

Easier to catch them than if they are in the default debug log.

Added Profiler::debugGroup() as wrapper to wfDebugLog(), as
there already is Profiler::debug() for wfDebug(), so that
there won't be a fatal error if the error happens before the
inclusion of GlobalFunctions.php and converted other calls
to wfDebugLog() to use it.

Change-Id: Ie8481a2e13a94efa0248dd5a36b6b1a22811817e
Merge "New 'profileerror' log group for profiling errors"