Martin von Zweigbergk <martinvonz@google.com> [Mon, 13 Feb 2017 16:03:05 -0800] rev 31177
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".