Add libroken as its own library

Add libroken as its own library

Include libroken as a library in its own right, so that the whole
of the code can benefit from it. This change purely adds libroken
for the Unix build system. It doesn't replace those pieces of
libroken in hcrypto or util, or enable it for Windows.

There is also the option of using a system-install libroken, if one is
found at configure time.
  *) If --with-libroken=yes, or is not supplied than a system library
     will be used if suitable. Otherwise, we'll use the internal
     libroken
  *) If --with-libroken=/path/to/installation then the libroken at
     that path will be used. If there is no libroken there, or it
     is not suitable, an error will be returned
  *) If --with-libroken=internal then the internal libroken is used,
     regardless of what is present on the system.

We deliberately do not provide installed headers for the internal
libroken. If other applications wish to make use of libroken, then
they should use the Heimdal one, rather than piggybacking on ours.

Change-Id: Iff01e1e17090404cc8e4783108ae8a8784170918
Reviewed-on: http://gerrit.openafs.org/3191
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>