Add support for platforms without fnmatch.

This uses gnulib so you will need to have a copy in order
to run autogen.sh (but not to build from a tarball). Either
arrange for gnulib-tool to be in your path or set the
environment variable GNULIB_TOOL to point to its location.

 /alloca.m4

 /extensions.m4

 /fnmatch.m4

 /gnulib-common.m4

 /gnulib-comp.m4

 /gnulib-tool.m4

 /include_next.m4

 /mbstate_t.m4

 /stdbool.m4

 /wchar.m4

 /wctype.m4

 /wint_t.m4