[mythtvnz] mhegepgsnoop updates

[Stephen Worthington]

Having worked through the problems Robert was having getting
mhegepgsnoop working, I have done some updated versions of the
required files.

There is an updated version of mhegepgsnoop.py that fixes the
documentation of the -m option, which does not work if you leave
whitespace between the -m and the double quote starting the string
that follows it:

http://www.jsw.gen.nz/mythtv/mhegepgsnoop-0.7.3.py

There are no code changes, only documentation changes.

There is an updated version of do_mhegepgsnoop.sh.  This fixes two
bugs and has more help text:

http://www.jsw.gen.nz/mythtv/do_mhegepgsnoop3.sh

The first bug was that the commented out MYTHCONFDIR= line requires
"export" in front of it.  This was the main cause of the problems
getting Robert's setup working.

The second bug is that the return code from running mythfilldatabase
was not being reported back to systemd so if mythfilldatabase failed,
systemd was reporting that epg.service succeeded.