upgrade: extract code in its own module Given about 2/3 or 'mercurial.repair' is now about repository upgrade, I think it is fair to move it into its own module. An expected benefit is the ability to drop the 'upgrade' prefix of many functions. This will be done in coming changesets.

bundle2: move the 'close' method off the unpackermixin This method is unrelated to unpacking and only used by the unbundle20 class. We move it there for clarity.

bundle2: clarify the docstring of unpackermixin methods The unpackermixin is a utility used to implement the bundle2 protocol. It should not be used when writing part handlers. We update the docstring to clarify this.

bundle2: add documention to 'part.addparams' There are some non-obvious limitations on the parameters of this method. Add some documentation where people will likely look to understand how to use this API.

test-patchbomb: disable sendmail tests on Windows These tests were failing, and there isn't a trivial way to execute a script on Windows [1]. [1] https://www.mercurial-scm.org/pipermail/mercurial-devel/2017-April/096497.html

show: fix corrupt json output with no bookmarks

show: tweak plain abort language for clarity