convert: replace repr() by pycompat.byterepr() in cvsps.py (issue6789)

convert: change socket mode from b'r+' to 'rwb' in cvs.py (issue6789) 'r+' mode used to open sockets for read/write operations, but '+' is not supported in Python 3. We're using bytes with these sockets everywhere, so the mode should have 'b'. But the mode argument has to be str, not bytes.

convert: turn the last str regex into bytes in cvs.py (issue6789) Since root is bytes, the regular expression should also be bytes.

worker: avoid reading 1 byte at a time from the OS pipe Apparently `pickle.load` does a lot of small reads, many of them literally 1-byte, so it benefits greatly from buffering. This change enables the buffering, at the cost of more complicated interaction with the `selector` API. On one repository with ~400k files this reduces the time by about ~30s, from ~60 to ~30s. The difference is so large because the actual updating work is parallellized, while these small reads are bottlenecking the central hg process.

diffutil: rewrite an ersatz ternary operator for building diffopts.text Pytype tends to get confused by these, but the real problem here is that if the caller passes `opts={}` as TortoiseHg has been doing, that is set as the value for `diffopts.text` when in reality it expects a boolean. When `None` is passed explicitly, the default value in `mdiff.defaultopts` is assigned.

mdiff: add a __str__ method to diffopts This makes it easier to debug by just formatting the object into `%s` to see the members and state, instead of the class and memory address.

debugshell: allow TortoiseHg builds to exit with the usual `quit()` command I've long been annoyed that `quit()` only randomly worked to exit the interpreter. When that happens, Ctrl+C doesn't work either (it simply prints "KeyboardInterrupt"), so then you have to `import sys` and `sys.exit()`. But it turns out that the behavior isn't random and it depended on which `hg.exe` was picked up on PATH first, because py2exe disables site initialization. I wasn't able to persuade the maintainer to allow an opt-in to initialization[1], but this works around it so that the behavior is now consistent however `hg.exe` is built. TortoiseHg 6.3.3 will be the first build that includes the site package, so handle the ImportError. [1] https://github.com/py2exe/py2exe/issues/154