libpulse: Always return a three part version number in API calls.

libpulse: Always return a three part version number in API calls.

For both the headers and the library we should provide clean, three part
strings as this has been what we've previously done in the past
and some external systems apparently rely on this format. While it's not
something we've officially commented on before, there is no real advantage
to us to change it so let's not try to tidy things up too much
considering some third party apps (e.g. Skype) seem to dislike a two
part version string.