diffhelpers: naming and whitespace cleanup

diffhelpers: remove C implementation in favor of pure Python version

patch: stop using cext.diffhelpers The C implementation has a couple of memory bugs, and lacks error handling which could lead to SEGV. I could fix them one by one (and I mostly finished that), but the performance gain provided by cext.diffhelper is quite low. Besides, diffhelpers.addlines() calls back Python, linereader.readline(), from the innermost loop. $ hg export -R mozilla-central 0:100 > patch $ ls -lh patch -rw-r--r-- 184M patch $ hg init repo && hg -R repo import patch --time --bypass (cext) time: real 34.970 secs (user 32.720+0.000 sys 2.230+0.000) (pure) time: real 35.950 secs (user 33.600+0.000 sys 2.330+0.000) So, let's simply use the pure Python implementation.

diffhelpers: port docstrings from cext to pure I'll remove the C implementation.

py3: get rid of character access from pure.diffhelpers 's' is a result of readline(), so 'c == "\n"' means 's == "\n"'.

lfs: handle paths that don't end with '/' when inferring the blob store While here, I also checked the lfs.url config directly instead of testing the scheme, as requested by Yuya.

lfs: infer the blob store URL from an explicit push dest or default-push Unlike pull, the blobs are uploaded within the exchange.push() window, so simply wrap it and swap in a properly configured remote store. The '_subtoppath' field shouldn't be available during this window, but give the passed path priority for clarity. At one point I hit an AttributeError in one of the convert tests when trying to save the original remote blobstore when the swap was run unconditionally. I wrapped it in a util.safehasattr(), but then today I wasn't able to reproduce it. But now the whole thing is tucked under the requirement guard because without the requirement, there are no blobs in the repo, even if the extension is loaded.

lfs: infer the blob store URL from an explicit pull source I don't see any easier way to do this because the update part of `hg pull -u` happens outside exchange.pull(), and commands.postincoming() doesn't take a path. So (ab)use the mechanism used by subrepos to redirect where subrepos are pulled from when an explicit path is given. As a bonus, this should allow lfs blobs to be pulled into a subrepo when it is checked out. An explicit push path can be handled within exchange.push(). That can be done next, outside of this dirty hack.