<bugfix>Fixed typo in parse/update for parameter types introduced in recent commit</bugfix> <bugfix>#623</bugfix>
<bugfix>Fixed typo in parse/update for parameter types introduced in recent commit</bugfix>
<bugfix>#623</bugfix>

There was a typo and an issue with the private fields not being set correctly in the revised parse_db_type and update_db_type methods.

core/vistrail/module_param.py:
  - ModuleParam.parse_db_type: check if db_type is None and set private fields to None
  - ModuleParam.update_db_type: identifer -> identifier
  - TestModuleParam.test_parse: new test

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