Add a libraries-only build target.
Add a libraries-only build target.

This is useful for GUI (TSVN) clients who may not need or want to
build all the exe's, tests, etc.

Suggested by: Stefan King <tortoisesvn@gmail.com>
Review by: Daniel Rall <dlr@collab.net>

* build.conf
 Add a __LIBS__ build target for our libraries and their dependencies.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion