merge LocalComputeFStat() into ComputeFStat() function

   - passes local jenkins
   - refs #543
XLALSetupFstat_Demod: new parameter demodHL to allow selecting hotloop variant

  - pure API change for now, no functionality attached yet
  - refs #543
fixup! XLALSetupFstat_Demod: new parameter demodHL to allow selecting hotloop variant

- define in C source, so value is set when LALPulsar is compiled
- refs #543
XLALSFTdataFind: change convention for SFT being in a GPS interval [start,end)

- New convention is if SFT interval [epoch,epoch+Tsft) is within GPS interval:
    start <= sft.epoch && sft.epoch + sft.Tsft <= end
  This is internally implemented in the function interval_in_GPS_range(),
  and exposed publically in the function XLALSFTinGPSrange().
- This is now consistent with the --minStartTime and --maxEndTime arguments
  of LALApps codes, e.g. CFSv2. Old convention was *not* consistent with this,
  as it considered only SFT start times:
    start <= sft.epoch && sft.epoch < end
  so --maxEndTime was really being treated as a maximum SFT *starting* time.
- Renamed SFTConstraints fields to less ambiguous minStartTime and maxEndTime.
- Refs #1286
ExtrapolatePulsarSpins: XLALified LALExtrapolatePulsarSpins()

- As usual LAL function is now just a wrapper
- Hide old LAL functions from Doxygen, move documentation to XLAL functions
- Refs #1285
ExtrapolatePulsarSpins: minor comment fixup

- Refs #1285