Import net/unbound package from Subversion

This is an import of the net/unbound package from Subversion
revision 40658 (May 2, 2014). The only change is the addition of
PKG_LICENSE and PKG_LICENSE_FILE to Makefile. Unbound 1.4.22 is
the current upstream release.

Signed-off-by: Michael Hanselmann <public@hansmi.ch>