CRS/CRIU: added CRIU as new CRS component

To be able to checkpoint/restart using criu (criu.org) a new
CRS component is added which is based on criu. This first commit
provides the minimal set of functions and configure script options
to enable --with-criu and link against libcriu.so.
No actual checkpoint/restart functionality is yet implemented.
This is only the framework which needs to be filled with the
actual functionality.
CRS/SELF: fix compiler warning: variable 'callback_matched' set but not used