Master

neaer typo in FCSInterface.c corrected (print statement) 

FCS_2_SQRTPI in documentation file doc/interface.tex set to value of src/FCSDefinitions.h and typo corrected

removal of constants like M_E from lib/p3m/utils.h and lib/p3m/error_estimate.c to prevent redundancy and improve maintenance. Please use the constants from FCSDefinitions.h like FCS_E. current usages were replaced by FCS_constants

include for FCSDefinitions.h added in error_estimate.c and utils.h, surrounded with ifndef FCS_PI.