Renamed [un]install goals to [un]avail.

The [un]install make goals have a rather fixed meaning for *ix users. The simple
symlinks provided here don't match the expectations users have from [un]install.
Therefore it is appropriate to rename them to "something" not tied to specific
expectations.
Have 'avail' not be dependent on 'all'.

There are two reasons for removing this dependency:
- If someone does 'make avail' on the top level Makefile he ends up with
  binaries but without libraries - not nice. Better do just "nothing" and
  have hin understand that he needs to do 'make [all]' on the top level
  Makfile first.
- If 'make avail' is done via 'sudo' it isn't desirable to do a large amount
  of work as root.
BTW: I wasn't sure if this dependency is a good thing in the first place
but I saw it in many examples ('install' depending on 'all') so I did it too.