<ticket>#336</ticket> <bugfix>Fix upgrades when module's version does not exist.</bugfix>
<ticket>#336</ticket>
<bugfix>Fix upgrades when module's version does not exist.</bugfix>

The preliminary upgrade mechanism fails when module.version is None.
We now check for the this and use core.utils.versions_increasing to
compare versions.

core/vistrail/pipeline.py:
  - Pipeline.ensure_modules_are_on_registry.find_descriptors: check if
    module.version is None and use versions_increasing to compare
    versions



hjanime/VisTrails,VisTrails/VisTrails,Nikea/VisTrails,minesense/VisTrails,minesense/VisTrails,celiafish/VisTrails,celiafish/VisTrails,VisTrails/VisTrails,VisTrails/VisTrails,Nikea/VisTrails,Nikea/VisTrails,minesense/VisTrails,hjanime/VisTrails,VisTrails/VisTrails,celiafish/VisTrails,hjanime/VisTrails,minesense/VisTrails,VisTrails/VisTrails,celiafish/VisTrails,minesense/VisTrails,Nikea/VisTrails,hjanime/VisTrails,hjanime/VisTrails