Only set variable_indices for arrays to not erroneously identify "t" as a postsynaptic variable.
Use a simpler propagation algorithm in numpy for code that does only refer to synaptic variables
Update the miniconda version used for testing in travis
... and don't forget to update the miniconda version for Python3 as well
Merge pull request #175 from brian-team/numpy_synapses

Simpler synaptic propagation in numpy