Try a local installation of libcrypto

If the distro-provided libcrypto is too old, then try a local
installation at /usr/local.

For example, this is needed to make attic run on Debian Squeeze,
which has an unsupported libcrypto (0.9.8), by also installing
a newer, supported version of libcrypto at /usr/local (e.g. with
the standard "./configure, make, make install" procedure)