patch.py: re-add the ability to use an external patch program
This is now invoked by default only if ui.patch is set. Otherwise, we
use our built-in patch. If that fails because it can't find any valid
hunks, we'll fall back to trying the external patch command.
#!/bin/sh
hg init
echo a > a
hg ci -d '0 0' -Ama
hg an a
echo "[ui]" >> $HGRCPATH
echo "strict=True" >> $HGRCPATH
hg an a
hg annotate a
echo % should succeed - up is an alias, not an abbreviation
hg up