Add more configure stuff for LXT and FST.

 * Add AC_FUNC_FSEEKO.
 * Add --enable-pthread to write FST in parallel.
 * Add --enable-judy to use Judy instead of builtin Jenkins for FST.

any thought?

P.S.
`make check` looks ok to me on cygwin.
there is no regression for LXT and FST functions triggered by `make check` ATM?