Fix optional dependencies in OMERO formula

These changes should re-enable Ice 3.4 installation which was broken
Rename Ice 3.4 formula as zeroc-ice34

Reduces confusion with mainstream ice formula which is building 3.5
Add genshi dependency for develop version of OMERO formula
Use --with-java and --with-python options for zeroc-ice34
Build zeroc-ice34 with Python if using brew install omero --with-ice34
Install Python libraries in Ice default #{prefix}/python
Use berkely-db46 for ZeroC Ice 3.4 formula
Merge pull request #31 from sbesson/ice34

Ice 3.4
Merge pull request #32 from sbesson/omero_genshi

Add genshi dependency for develop version of OMERO formula