bump lib and hooks versions

This is slightly more complicated than the usual +1 and be done with it. The problem is that as we kick off 1.9 development, we're essentially sure there will be some number of stable 1.8.x releases. We don't want to clash with the versions.

Here's what I propose. For hooks version, we can encode the kea version on hook version. We For 1.9.0, we can use 10900. We had 10 minor revisions in 1.7, so we need to reserve 2 digits for each major, minor and release versions. That's ok, though, as hook version is an int, so we have plenty of values to go through.

For the libtool version, we should do the same as BIND 9. We should jump forward and reserve some number (10?) of potential releases. If previous experience means anything, we can expect to have 3-5 releases before we release the next stable branch.