SFTutils: new API function XLALExtractBandFromSFT()

- and used this in XLALExtractBandFromSFTVector()
- passes 'make check'
LFTandTSutils: new sinc-interpolator function for (COMPLEX8) time-series

- XLALSincInterpolateCOMPLEX8TimeSeries()
- also adds an appropriate unit-test
- refs #535
LFTandTSutils: new Dirichlet interpolator functions

- XLALDirichletInterpolateCOMPLEX8FrequencySeries() and
  convenience wrapper XLALDirichletInterpolateSFT()
- contains unit tests, comparing Dirichlet interpolation versus
  direct upsampling (via zero-padding)
- refs #535