merge: use operation-provided labels (ex: dest/source) in several merge-tools

merge: use operation-provided labels (ex: dest/source) in several merge-tools

Tools that did not use labels already, used only one, or used some label other
than the exact strings of "local" or "other" were unmodified.  Cases that used
the label "base" were modified as well, if they were otherwise changed in this
CL; "merged" was *not* changed.

There are other possible changes we might want to make, but I didn't:
- bcompare (linux and osx) uses the labels "parent1" and "parent2" instead of
  "local" and "other", so it was left alone, even though beyondcompare3
  (windows) *was* changed.
- araxis used the labels "Other", "Base", and "Local :$local", so it was also
  left alone.
- UltraCompare didn't provide a label for 'local', just for 'base' and 'other',
  so it was left alone.

Differential Revision: https://phab.mercurial-scm.org/D2012

--- a/mercurial/default.d/mergetools.rc	Wed Jan 17 17:35:05 2018 -0800
+++ b/mercurial/default.d/mergetools.rc	Sat Jan 20 15:33:48 2018 -0800
@@ -1,7 +1,7 @@
 # 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.args=--auto --L1 $labelbase --L2 $labellocal --L3 $labelother $base $local $other -o $output
 kdiff3.regkey=Software\KDiff3
 kdiff3.regkeyalt=Software\Wow6432Node\KDiff3
 kdiff3.regappend=\kdiff3.exe
@@ -26,7 +26,7 @@
 gpyfm.gui=True
 
 meld.gui=True
-meld.args=--label='local' $local --label='merged' $base --label='other' $other -o $output
+meld.args=--label=$labellocal $local --label='merged' $base --label=$labelother $other -o $output
 meld.check=changed
 meld.diffargs=-a --label=$plabel1 $parent --label=$clabel $child
 
@@ -35,7 +35,7 @@
 tkdiff.priority=-8
 tkdiff.diffargs=-L $plabel1 $parent -L $clabel $child
 
-xxdiff.args=--show-merged-pane --exit-with-merge-status --title1 local --title2 base --title3 other --merged-filename $output --merge $local $base $other
+xxdiff.args=--show-merged-pane --exit-with-merge-status --title1 $labellocal --title2 $labelbase --title3 $labelother --merged-filename $output --merge $local $base $other
 xxdiff.gui=True
 xxdiff.priority=-8
 xxdiff.diffargs=--title1 $plabel1 $parent --title2 $clabel $child
@@ -44,7 +44,7 @@
 diffmerge.regkeyalt=Software\Wow6432Node\SourceGear\SourceGear DiffMerge\
 diffmerge.regname=Location
 diffmerge.priority=-7
-diffmerge.args=-nosplash -merge -title1=local -title2=merged -title3=other $local $base $other -result=$output
+diffmerge.args=-nosplash -merge -title1=$labellocal -title2=merged -title3=$labelother $local $base $other -result=$output
 diffmerge.check=changed
 diffmerge.gui=True
 diffmerge.diffargs=--nosplash --title1=$plabel1 --title2=$clabel $parent $child
@@ -72,7 +72,7 @@
 tortoisemerge.priority=-8
 tortoisemerge.diffargs=/base:$parent /mine:$child /basename:$plabel1 /minename:$clabel
 
-ecmerge.args=$base $local $other --mode=merge3 --title0=base --title1=local --title2=other --to=$output
+ecmerge.args=$base $local $other --mode=merge3 --title0=$labelbase --title1=$labellocal --title2=$labelother --to=$output
 ecmerge.regkey=Software\Elli\xc3\xa9 Computing\Merge
 ecmerge.regkeyalt=Software\Wow6432Node\Elli\xc3\xa9 Computing\Merge
 ecmerge.gui=True
@@ -93,7 +93,7 @@
 filemergexcode.gui=True
 
 ; Windows version of Beyond Compare
-beyondcompare3.args=$local $other $base $output /ro /lefttitle=local /centertitle=base /righttitle=other /automerge /reviewconflicts /solo
+beyondcompare3.args=$local $other $base $output /ro /lefttitle=$labellocal /centertitle=$labelbase /righttitle=$labelother /automerge /reviewconflicts /solo
 beyondcompare3.regkey=Software\Scooter Software\Beyond Compare 3
 beyondcompare3.regname=ExePath
 beyondcompare3.gui=True
@@ -113,7 +113,7 @@
 bcomposx.priority=-1
 bcomposx.diffargs=-lro -lefttitle=$plabel1 -righttitle=$clabel -solo -expandall $parent $child
 
-winmerge.args=/e /x /wl /ub /dl other /dr local $other $local $output
+winmerge.args=/e /x /wl /ub /dl $labelother /dr $labellocal $other $local $output
 winmerge.regkey=Software\Thingamahoochie\WinMerge
 winmerge.regkeyalt=Software\Wow6432Node\Thingamahoochie\WinMerge\
 winmerge.regname=Executable