Longbow v1.3.1

The changes in this release are summarised below:

1. For machines running SGE a new parameter to control the flag used on
   the -pe directive has been implemented. This parameter is "sge-peflag"
   and has a default value of "mpi", if your cluster requires something
   different then use this parameter in a configuration file to set it.

2. Some cases on SGE clusters, it can be set that even if a job needs
   only 1 core that the -pe mpi #cores must be set. A new flag called
   "sge-peoverride" will make this happen, just provide "sge-peoverride =
   true" in a configuration file to enable.

3. Fixed a problem where Longbow would exit when no jobs are running,
   this was fixed in PBS but not in other schedulers. It is now fixed in
   all supported schedulers.

4. The import statements that looked pretty nasty across the library
   have been changed for nicer more pythonic ones.

5. Some refactoring to get rid of pylint warnings about not using lazy
   logging.

6. Ability to add script calls into the job submission script that is
   created by Longbow. The parameter "scripts" should be used, for multiple
   script references then a comma separated list should be provided. Just
   add something like this to your configuration file "scripts = source
   /some/file" or "scripts = source /first/file, source /second/file"

7. Fix a problem when using job configuration files and not referencing
   a resource, what should have happened is that Longbow should choose the
   default (top one in hosts.conf). But it crashed with a KeyError
   exception, this is now fixed.