Fix listmodes when the config does not specify a wildcard size entry.
Merge pull request #899 from SaberUK/insp20+fix-listmode-limits

[2.0] Fix listmodes when the config does not specify a wildcard size entry.
Fix pkg-config not being used for OpenSSL on non-FreeBSD systems.
Add a work around for trampling over PKG_CONFIG_PATH.

The extend_pkg_path method will be removed in 2.2 as it
causes problems with non-standard pkg-config paths. This
commit adds a workaround until that happens.