MFC r218719 (by hand, depends on r209592):

MFC r218719 (by hand, depends on r209592):
Make a linux_rt_sigtimedwait() system call is actually working.

1) Translate the native signal number in the appropriate Linux signal.
2) Remove bogus code, which can lead to a panic as it calls
   kern_sigtimedwait with the same ksiginfo.
3) Return the corresponding signal number.

git-svn-id: svn://svn.freebsd.org/base/stable/8@219202 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f