allow __have_feature__ to check for ENABLE_ options * __have_feature__.m: Handle ENABLE_ options. * mex_demo.c, oct_demo.cc: Update note about octave_config_info. * toplev.cc (Foctave_config_info): For ENABLE_ options, store logical values instead of true/false or yes/no strings in struct. * computer.m: Change use of octave_config_info ("ENABLE_64").

gnulib-hg = gnulib-hg