Strip trailing whitespace

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Move xau from Requires to Requires.private in printproto.pc

The xau headers are required because Print.h has #include <X11/Xauth.h>
for the definition of the Xauth typedef, but software including this
header doesn't necessarily need to link with libXau.

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>