Fix rfc3195 configure check

Newer versions of liblogging were restructured and now also contain
other components besides rfc3195. As a result the original liblogging
library was split and the rfc3195 component was renamed to
liblogging-rfc3195 along with its pkg-config file.

Update the configure check accordingly.
Since we require liblogging >= 1.0.1 anyway, don't add a fallback check
for the old pkg-config name.

Fixes #30