chg: removed 'extern "C"' around declaration of feOptHelp and feGetOptValue

proposed fix from Hans
declaring functions as C functions caused some problems during the compilation
on cygwin systems because certain object files expected them to be c++ functions
unsure why they were declared as C functions to begin with
Merge pull request #370 from YueRen/spielwiese

chg: removed 'extern "C"' around declaration of feOptHelp and feGetOptValue