merge: save merge part labels for later reuse We permit the caller of merge operations to supply labels for the merge parts ("local", "other", and optionally "base"). These labels are used in conflict markers to reduce confusion; however, the labels were not persistent, so 'hg resolve' would lose the labels. Store the labels in the mergestate.

ui: add prompt argument to write (issue5154) (API) When code like filemerge._iprompt calls ui.prompt, it expects the user to see the output in addition to getting the prompt. Other code such as histedit may call ui.pushbuffer, but its goal is not to interfere with prompts, so this commit adds an optional prompt flag to ui.write and has _readline include that argument. ui.promptchoice calls ui.prompt which calls ui._readline. This commit also updates hgext.color.write.

hg: perform update after pulling during clone with share (issue5103) This is a graft of 60adda1a0188 and a4692267bc2d from the default branch. Combined, they address a bug with pooled shared storage where an update may not update to the most recent revision when performing a `hg clone`. The patches should have been written against the stable branch in the beginning. I screwed up.