record: use "ui.extractchoices()" to get the list of available responses Before this patch, record extension gets the list of available responses from online help document of "hg record" in the tricky way, even though the value passed to "ui.promptchoice()" has enough (maybe i18n-ed) information. This patch uses "ui.extractchoices()" to get the list of available responses.

ui: add "extractchoices()" to share the logic to extract choices from prompt

branchmap: use set for update code We are doing membership test and substraction. new code is marginally faster.