Readcell cannot handle names like 'axon[1]'

Created by: subhacom

Refer to TESTS/regression/moose_readcell.g

Compartment names like axon[1] are not handled properly. The reason is that 'axon[1]' is assumed to exist because 'axon' does (in this particular example). Go to ReadCell.cpp:298 in revision 450.

Reported by: niraj_