fix compile errors on readdir()-deficient platforms

fix compile errors on readdir()-deficient platforms

* Cygwin does not have "struct dirent.d_type".  Check for that in the
configure script and use stat() to test for directory-ness instead.
git-archimport-id: srvx@srvx.net--2004-srvx/srvx--devo--1.3--patch-50