Fix AT91SAM9260 to work with PA rather than VA device addresses.
In _pthread_kill(), if passed pthread is current thread, do not send
the signal second time, by adding the missed else before if statement.

While there, postpone initializing local curthread variable until
passed signal number is checked for validity.

Submitted by:	John Wolfe <jlw@xinuos.com>
PR:	threads/186309
MFC after:	1 week