meld: enable auto-merge

This tells meld to resolve trivial conflicts before presenting the
user with the remaining conflicts.

This was attempted 5 years ago, but then --auto-merge was too new that
the patch was rejected out of concern that users still had an older
version of meld installed [1]. Maybe it's safe to assume that they
have a newer version now.


 [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2013-April/050084.html

Differential Revision: https://phab.mercurial-scm.org/D4665

mercurial/default.d/mergetools.rc

@@ -26,7 +26,7 b' merge.priority=-100'
 gpyfm.gui=True
 
 meld.gui=True
-meld.args=--label=$labellocal $local --label='merged' $base --label=$labelother $other -o $output
+meld.args=--label=$labellocal $local --label='merged' $base --label=$labelother $other -o $output --auto-merge
 meld.check=changed
 meld.diffargs=-a --label=$plabel1 $parent --label=$clabel $child