Certain programs, like zim, calibre and now also apparently mercurial,
rely on sys.argv[0] providing not just the script name but the full
path.
The Python docs [1] state the following on the matter:
> argv[0] is the script name (it is operating system dependent whether
this is a full pathname or not).
Therefore, scripts should not expect to receive a full path.
Unfortunately some do. While this can be considered a bug, there doesn't
seem any reason not to provide the full path. Therefore we now provide
the full path.
[1]
https://docs.python.org/3.5/library/sys.html?highlight=sys.argv#sys.argv
