postgis to oracle geometry conversion

Hi @laurenz ,

Here comes the postgis -> oracle conversion. The code is still untested, I should have my access back to an oracle server later this week (I tried to set one up on my machine with oracle xe, but oracle admin is really time consuming, especially when you are not a DBA).

I'm not sure that pallocing the geometry is the right thing to do: since the OCIArrays are created with OCIObjectNew, maybe we should do the same for oracle geometry. This allocation also clutters the code.

I also put a couple of asserts that I have to convert into proper postgres errors 

If you have suggestions/improvements, you can PR me back.