rebase: un-wrap function signature since it fits in 80 columns

py3: exclude pywatchman from test-check-py3-compat.t Exclude pywatchman from py3 test. They have already worked on Python 3 compatibility https://github.com/facebook/watchman/pull/247

py3: update test-check-py3-compat.t This part of test runs only on py3. This change was introduced by 16f4b341288d.

shelve: choose a legal shelve name when no name is passed (issue5112) Currently if our branch name contains '\' or starts with '.', shelve chooses an illegal shelve name. This behaviour is not good as it itself is choosing something which it won't accept further. We can raise errors if user passes a name which is illegal. After this patch, if '\' is contained in branch name or bookmark name, it will be replaced by '_' while choosing a shelve name and if they starts with '.', the first '.' is replaced by '_'.

shelve: add tests to ensure illegal shelve names are avoided We avoid '.' as the first letter of shelve name so that we don't create hidden file. We also avoid slashes in name so that we don't form a new directory

py3: replace sys.executable with pycompat.sysexecutable sys.executable returns unicodes on Python 3. This patch replaces occurences of sys.executable with pycompat.sysexecutable.

py3: have bytes version of sys.executable sys.executable on Python 3 returns unicodes and we want bytes. So this patch adds a new pycompat.sysexecutable which returns bytes by encoding using os.fsencode() since it is path variable.

py3: use pycompat.getcwd instead of os.getcwd