Make it possible to disable filtering for a pattern.
Rationale: Apparently there were no way to disable for example win32text extension locally.
RFC: Can it already be done another way?
#!/bin/sh
echo '[Section]' >> $HGRCPATH
echo 'KeY = Case Sensitive' >> $HGRCPATH
echo 'key = lower case' >> $HGRCPATH
hg showconfig Section