update: add experimental config for default way of handling dirty wdir This allows the user to set e.g. experimental.updatecheck=abort to abort update if the working directory is dirty, but still be able to override the behavior with e.g. --merge when needed. I considered adding a --mergelinear option to get back the old behavior even when experimental.updatecheck=abort is set, but I couldn't see why anyone would prefer that over --merge. The default is read in hg.updatetotally(), which means it also applies to "hg pull -u" and "hg unbundle -u".

update: accept --merge to allow merging across topo branches (issue5125)

merge: combine the "merge" cases in docstring table

merge: combine "dirty" cases in docstring table

merge: clarify non-linear default updates in docstring table Non-linear updates won't happen by default, regardless of -c/-C.

merge: combine the two "can't happen" cases in docstring table

merge: move "incompatible options" case first in docstring table

merge: make "linear" an input in docstring table Instead of having two ouputs, it seem simpler to have an addition input. This will allow further simplification.

merge: drop redundant column in docstring table The "same" and "cross" columns now have the same values, so let's combine them into "non-linear".

merge: drop obsolete non-linear cases from docstring table Since 6b1fc09c699a (update: change default destination to tipmost descendant (issue4673) (BC), 2016-02-02), non-linear updates can no longer happen if the user doesn't specify a destination, so we can drop these case from the table in the docstring of merge.update().