help: fix extension commands help in keyword search
This patch fixes the synopsis shown for extension commands in keyword search
results. A previous patch erroneously caused the extension synopsis to be shown
instead.
Test cases for keyword search are missing, so I added a one.
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown