merge: make 'keep' message more descriptive
Most merge action messages don't describe the action itself, they
describe the reason the action was taken. The only exeption is the 'k'
action, for which the message is just "keep" and instead there is a
code comment folling it that says "remote unchanged". Let's move that
comment into the merge action message.
$ echo 'raise Exception("bit bucket overflow")' > badext.py
$ abspath=`pwd`/badext.py
$ cat <<EOF >> $HGRCPATH
> [extensions]
> gpg =
> hgext.gpg =
> badext = $abspath
> badext2 =
> EOF
$ hg -q help help
*** failed to import extension badext from $TESTTMP/badext.py: bit bucket overflow
*** failed to import extension badext2: No module named badext2
hg help [-ec] [TOPIC]
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