Allow vhpiLogicVal and vhpiLogicVecVal as aliases of vhpiEnumVal and vhpiEnumVecVal

According to the VHPI spec, signals with type std_logic, std_ulogic, or bit, and arrays of those types should use vhpiLogicVal or vhpiLogicVecVal as the native format.
Merge pull request #136 from nickg/logicval

Allow vhpiLogicVal and vhpiLogicVecVal as aliases of vhpiEnumVal and vhpiEnumVecVal