P2NFFT: add sym and ec far field regularization for mixed periodicity
Merge branch 'master' of https://github.com/scafacos/scafacos
add fcs_ prefixes
avoid warnings about uninitialized regularization flags
always use last non-nan/inf/zero value of inc_bessel_k approximation
Merge branch 'master' of https://github.com/scafacos/scafacos
1dp-P2NFFT: fix NaN of inc. BesselK with large arguments
1dp-P2NFFT: avoid underflows in gsl_sf_gamma_inc for large arguments
avoid underflow in gsl_sf_gamma_inc
fixed error in bessel_k.c : if fabs(val_new)<eps
use taylor approximation in bessel_k.c for nu=0, x and y small
included upper bound for modified bessel function