fix log_filter, remove now superfluous SAGA_PTYDEBUG

Hi Ole,

to disable the PTY log messages, please set

   export SAGA_LOG_FILTER='!PTYShell'

in your env, and they will disappear.
remove dead code
cosmetics on shell job management

One of the failures reported was caused by the recently introduced job purge --
I fixed the tests to cater for that.  I am not yet sure what is up with the
lonestar prolems reported by melissa - need more tests
Merge branch 'fixes' of github.com:saga-project/saga-python into fixes
ignore errors from purge
attempt to fix bogus resource shortage problem
Merge branch 'devel' into fixes
set large gc timout until #75 is fixed
Merge branch 'fixes' of github.com:saga-project/saga-python into fixes
Ole, have a look at the ssh context docs...
Merge branch 'devel' into fixes

Conflicts:
	saga/adaptors/context/ssh.py
resolved conflict