histedit, i18n: replace '+' with concatenation to make hggettext happy

commands: fix typo in --graph description

revset, i18n: add translator comment to "only"

merge: improve notes for listing the bids for ambiguous merges

merge: tell the user when we are using bid merge Bid merge is a new rarely used feature that the user explicitly enabled - we should tell/warn when the user actually is using it, just like we tell when we not are using it. Give a message like note: merging 3b08d01b0ab5+ and adfe50279922 using bids from ancestors 0f6b37dbe527 and 40663881a6dd

merge: fix stray character in bid merge message

tests: better test coverage for bid merge Martin Geisler's test case revealed the previous message argument error.