testsuite::test_hpc_synapse - Basic tests on hpc synapses
(test_hpc_synapse) run -> NEST exits if test fails  

Test basic properties of HPC synapses as follows:

1. For all known synapses with _hpc ending and counterparts without _hpc
connect spike generator to one neuron with normal, one with _hpc synapse,
ensure that simulation yields identical membrane potentials.

2. Check that adding and freezing/thawing of nodes either is blocked or
does not affect results, i.e., that the TargetIdentifierIndicies are ok.
These tests proceed as follows:
1. Connect spike_generator to N neurons with different weights,
disable spiking in receptors. We use membrane potential after simulation
as indicator for through which synpse a neuron received input.
2. Build network once with plain static_synapse to get reference data.
3. Then build with respective test cases and compare.

Hans E Plesser, 2014-11-14