A note on modern git plus ancient meld ("wrong number of arguments")

[Jeff Epler <jepler@unpythonic.net>]

I note this just in case it helps someone else track down a similar
problem, not because I think any change needs to be made to git, as a
version of meld new enough to not be affected by this problem is 5 years
old.

At $DAYJOB, I recently encountered a problem after upgrading from (don't
laugh) git 1.7.1 to 1.7.8.3: one developer stated that meld failed to
run, instead displaying the error 'Wrong number of arguments (Got 5)'. 

We determined that this user was running a very old version of meld
(1.1.1) from his home directory, as opposed to the also very old system
version of meld (1.1.5).  It turns out that the check added in 
    f61bd9c mergetools/meld: Use '--output' when available
fails on meld 1.1.1, leading git to incorrectly believe the --output
flag is supporrted:
    $ meld-1.1.1 --output /dev/null --help >/dev/null 2>&1; echo $?
    0   # i.e., detected as supported
The test as written gives the correct ("not supported") result with meld
1.1.5:
    $ meld-1.1.5 --output /dev/null --help >/dev/null 2>&1; echo $?
    2   # i.e., detected as supported

so if you encounter the message 'Wrong number of arguments (Got 5)' from
meld, then check whether you have an ancient version of meld.  If for
some reason you can't upgrade to at least 1.1.5, maybe you'd find the
following configuration flags useful:
    [merge]
        tool = ancientmeld
    [mergetool "ancientmeld"]
        cmd = meld-1.1.1 \"$LOCAL\" \"$MERGED\" \"$REMOTE\"

Jeff