mergetools: add pointer to the usual filemerge path

contrib/mergetools.hgrc

@@ -1,50 +1,51
 # Some default global settings for common merge tools
 
 [merge-tools]
 kdiff3.args=--auto --L1 base --L2 local --L3 other $base $local $other -o $output
 kdiff3.regkey=Software\KDiff3
 kdiff3.regappend=\kdiff3.exe
 kdiff3.fixeol=True
 kdiff3.gui=True
 
 gvimdiff.args=--nofork -d -g -O $local $other $base
 gvimdiff.regkey=Software\Vim\GVim
 gvimdiff.regname=path
 gvimdiff.priority=-9
 
 merge.checkconflicts=True
 merge.priority=-10
 
 gpyfm.gui=True
 
 meld.gui=True
 
 tkdiff.args=$local $other -a $base -o $output
 tkdiff.gui=True
 tkdiff.priority=-8
 
 xxdiff.args=--show-merged-pane --exit-with-merge-status --title1 local --title2 base --title3 other --merged-filename $output --merge $local $base $other
 xxdiff.gui=True
 xxdiff.priority=-8
 
 diffmerge.args=--nosplash --merge --title1=base --title2=local --title3=other $base $local $other
 diffmerge.checkchanged=True
 diffmerge.gui=True
 
 p4merge.args=$base $local $other $output
 p4merge.regkey=Software\Perforce\Environment
 p4merge.regname=P4INSTROOT
 p4merge.regappend=\p4merge.exe
 p4merge.gui=True
 p4merge.priority=-8
 
 tortoisemerge.args=/base: $output /mine:$local /theirs:$other /merged:$output
 tortoisemerge.regkey=Software\TortoiseSVN
 tortoisemerge.gui=True
 
 ecmerge.args=$base $local $other --mode=merge3 --title0=base --title1=local --title2=other --to=$output
 ecmerge.regkey=Software\Elli\xc3\xa9 Computing\Merge
 ecmerge.gui=True
 
+filemerge.executable=/Developer/Applications/Utilities/FileMerge.app/Contents/MacOS/FileMerge
 filemerge.args=-left $other -right $local -ancestor $base -merge $output
 filemerge.gui=True