Add FreeBSD sources as a submodule

The current version corresponds to SVN r255967 of:

http://svn.freebsd.org/base/releng/8.2
Move files to match FreeBSD layout

Add compatibility with Newlib header files.  Some FreeBSD header files
are mapped by the translation script:

 o rtems/bsd/sys/_types.h
 o rtems/bsd/sys/errno.h
 o rtems/bsd/sys/lock.h
 o rtems/bsd/sys/param.h
 o rtems/bsd/sys/resource.h
 o rtems/bsd/sys/time.h
 o rtems/bsd/sys/timespec.h
 o rtems/bsd/sys/types.h
 o rtems/bsd/sys/unistd.h

It is now possible to include <sys/socket.h> directly for example.

Generate one Makefile which builds everything including tests.