py3: add an os.fsencode backport to ease path handling

py3: a second argument to open can't be bytes This fixes open(filename, 'r'), open(filename, 'w'), etc. calls. In Python 3, that second argument *must* be a string, you can't use bytes. The fix is the same as used with getattr() (where the second argument must also always be a string); in the tokenizer, where we detect calls, if there is something that looks like a call to open (and is not an attribute, so the previous token is not a "." dot) then make sure that that second argument is not converted to a `bytes` object instead. There is some remaining issue where the current transformer will also rewrite open(f('foo')). However this also affect function for which we perform similar rewrite ('getattr', 'setattr', 'hasattr', 'safehasattr') and will be dealt with in a follow up.

py3: make check-py3-compat.py import importlib only if necessary importlib isn't available on Python 2.6, and it isn't necessary for Py2 checks.

templater: handle division by zero in arithmetic For now, just turn it to an abort.

templater: provide arithmetic operations on integers The termwidth template keyword is of limited use without some way to ensure that margins are respected. Provide a full set of arithmetic operators (four basic operations plus the mod function, defined to match Python's // for division), so that you can create termwidth based layouts that match the user's terminal size

eol: store and reuse pattern matchers instead of creating in tight loop More "right" and more efficient.

eol: fix variable naming - call it _eolmatch instead of _eolfile It is not the file but a match object based on it.

parsers: move PyInt aliasing out of util.h The PyInt aliasing is only used by parsers.c. Since we don't want to encourage the use of PyInt parsing, move the aliasing to parsers.c.

osutil: use PyLongObject on Python 3 for listdir_slot This code looks performance sensitive. So let's retain PyIntObject on Python 2 and use PyLongObject explicitly on Python 3.

osutil: use PyLongObject in recvfds PyIntObject doesn't exist in Python 3. While PyIntObject is preferred on Python 2 because it is a fixed capacity and faster, the difference between PyIntObject and PyLongObject for scenarios where performance isn't critical or the caller isn't performing type checking shouldn't be relevant. So change recvfds to return a list of longs instead of ints on Python 2.