extdiff: reintroduce backward compatibility with manual quoting of parameters 72a89cf86fcd broke things ... and the following cleanups didn't fix all issues. It didn't work with the diffargs shipped in mergetools.rc with explicit quoting. Parameters would end up with being quoted twice - especially if they really needed quoting. To work around that, look for explicit quotes around the variables that will be substituted with proper quoting. Also accept an additional prefix so we can handle both --foo='$parent' and '--foo=$parent' It will however still fail if the user intentionally place the variable inside a quoted string, as in 'parent $parent is on the left' There is currently no good way to handle that, short of knowing exactly which quoting mechanism will be used.