in autoscan tables. Die if there are no spaces at all.
(scan_c_file): Use b instead of W so that keywords match at
the beginning and the end of the line.
(scan_sh_file): Likewise.
(scan_makefile): Likewise. Use B to match before `-l'.
(output): Suggest AC_CONFIG_HEADER if any C/C++ sources are
found.
* acidentifiers: Update macros for structure members st_blksize
and st_rdev.
