remove XLALInstrumentNameToLALDetector() stub
XLALSimDetectorStrainREAL8TimeSeries():  change detector param to const *
XLALSimDetectorStrainREAL8TimeSeries() allow arbitrary prefix length

the output time series' name has a max hard-coded length based on the assumption that instrument prefixes have 2 characters.  this patch makes it allocate the string on-the-fly in case that assumption isn't true.
XLALSimDetectorStrainREAL8TimeSeries() error path aesthetics
XLALSimDetectorStrainREAL8TimeSeries():  edit comments
XLALSimDetectorStrainREAL8TimeSeries()

check for failure in XLALComputeDetAMResponse()