json: implement {comparison} template
Similar to {filediff}, we abbreviate some property names to cut down on
string bloat.
#require serve killdaemons
#if windows
$ hg clone http://localhost:$HGPORT/ copy
abort: * (glob)
[255]
#else
$ hg clone http://localhost:$HGPORT/ copy
abort: error: Connection refused
[255]
#endif
$ test -d copy
[1]
$ python "$TESTDIR/dumbhttp.py" -p $HGPORT --pid dumb.pid
$ cat dumb.pid >> $DAEMON_PIDS
$ hg clone http://localhost:$HGPORT/foo copy2
abort: HTTP Error 404: * (glob)
[255]
$ "$TESTDIR/killdaemons.py" $DAEMON_PIDS