libextreemfs: added interrupt.h/cpp which add a scoped_lock/mutex like...

libextreemfs: added interrupt.h/cpp which add a scoped_lock/mutex like machanism to register a special signal handler to detect interruption. The corresponding functionality in execute_sync_request.h/cpp was removed, it now uses the new mechanism.

git-svn-id: https://xtreemfs.googlecode.com/svn/branches/mno-async_writes@2990 f8528748-c2c0-11dd-ba5c-d3b7c2b3b534