Fix parallel make problems.

Occasionally, make -j would fail due to missing includes, or other
unusual errors.

This was due to the 'cleantest' target, which was designed to force a
make clean when some change in the code would cause the typical
depedency checking to fail. Several targets in the main Makefile did
not depend upon cleantest, hence would run in parallel to it. By
adding the dependency, make -j runs happily now.

Review: https://reviewboard.asterisk.org/r/2418/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/1.8@384410 f38db490-d61c-443f-a65b-d21fe96a405b