merge with stable

convert: drastically speed up git conversions We would formerly exec git cat-file once for every commit, plus once for every tree and file we wnated to read. This switches to using git cat-file's batch mode, which is much, much, much faster. Using this new code, converting the git git repo to hg ran in 106 minutes on my machine. Using the stock mercurial, it required 1239 minutes. I believe this to be typical of the speedups we will see form this patch.

vim: use try catch in vim plugin to avoid conflicts

bundle2: raise BundleValueError error for stream level unsupported params This ensures both consistency and smooth propagation over the wire.

bundle2: support None parttype in BundleValueError This will be used for errors at the stream level.

bundle2: ignore advisory part with unknown parameters Advisory parts are advisory. If a handler exists but does not support the proper parameters, we can safely ignore it. Test has been updated to include this case.

bundle2: enforce all parameters in a part to be handled Once we picked a handler, we check that all mandatory parameter keys are properly supported. If not we raise an exception. We added a test for this case. The code now fails for any part with unknown mandatory parameters. We will ignore such errors for advisory parts in a later changeset.