Merge branch 'next'

* next:
  hygiene, properly cast int->char conversion
  hygiene, use modf() instead of fmod()
  fix, PEBKAC, don't finish a macro expansion with a semicolon
  fix, PEBKAC, include math.h for double funs in tzconv.c matlab contrib client
  minor, if --with-matlab succeeds, build tzconv.m matlab file
  minor, visit contrib/ directory
  chore, check for matlab upon --with-matlab
  chore, check for ldflags and libtool
  chore, import sxe-matlab.m4 (for SXE_CHECK_MATLAB)
  minor, import tzconv.c and tzconv.m, matlab convenience functions
  chore, import sxe-libtool.m4 (for SXE_CHECK_LIBTOOL)
  chore, import sxe-linker.m4 (for SXE_CHECK_LDFLAGS)
  chore, update sxe-compiler.m4 (use unserding's version)