Change return type of THaEvData::GetEpicsString to TString for consistency
Fix unused variable warnings (set but not used) courtesy of g++ 4.8
Cleanup return codes of THaRunBase and THaEvData

Previously, both interfaces could return implementation-dependent
error return codes, e.g. from EVIO or any other underlying IO system.
These internal codes are now translated to return codes that are specified
in the respective headers of the analyzer classes.

THaCodaData and derived classes still return raw EVIO codes. If these
need to be understood, then the implementation must include evio.h.
I want to avoid doing that in THaCodaData.h since CodaData is basically
another independent API that shouldn't explicitly depend on evio.h.

Also, noting that EVIO defines the event buffer type as uint32_t, we
change the type of the corresponding variables/parameters in THaEvData
and derived classes from Int* to UInt_t*. ROOT guarantees that UInt_t is
equivalent to uint32_t, i.e. 4 byte unsigned integer.