build-sys: no longer rebuild various bits and pieces such as man pages each time the Makefile changes

We don't do this for .c files either, even they are also influence quite
a bit by makefile settings. Given that XSLT is a lot slower then the
rest of the build let's make our build a bit faster if people end up
touching the Makefile.
bus: don't generate NameAcquired/NameLost messages in the library

The signals appear entirely redundant due to NameOwnerChange, hence
don't do them in the new library, instead leave them for the
compatibility bridge only.

Also, set the serial number for synthesized messages to (uint32_t) -1.
bus: synthesize local error reply when we cannot deliver a message to kdbus because the destination is unavailable
bus: whenever we notice the connection is terminated enter CLOSING state