chore, allow mex.h to be in include path right away, or in octave_CFLAGS/octave/
chore, use AC_CHECK_HEADERS so defines will be emitted
chore, include octave/mex.h in case the octave include path doesn't dive in that deep
chore, PEBKAC, now that pkg-config's gone AC_SUBST octave_CFLAGS and octave_LIBS ourselves
chore, actually mimic pkg-config by AC_ARG_VARing octave_{CFLAGS,LIBS}
minor, don't use hardcoded octave path, substitute ${libdir}
fix, PEBKAC, name directories without trailing slash
Merge branch 'contrib/mex-tzconv'

* contrib/mex-tzconv:
  fix, PEBKAC, name directories without trailing slash
  minor, don't use hardcoded octave path, substitute ${libdir}
  chore, actually mimic pkg-config by AC_ARG_VARing octave_{CFLAGS,LIBS}
  chore, PEBKAC, now that pkg-config's gone AC_SUBST octave_CFLAGS and octave_LIBS ourselves
  chore, include octave/mex.h in case the octave include path doesn't dive in that deep
  chore, use AC_CHECK_HEADERS so defines will be emitted
  chore, allow mex.h to be in include path right away, or in octave_CFLAGS/octave/