diffhelpers: remove unused return value from fixnewline() and addlines()

diffhelpers: move out of pure package

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.