Centralize function name. Update a comment while here.
s/__number/__num/ for code clarify but more to prevent localization of
__number if passed as the var_to_set argument.
Comment -- to go with NL global introduced (but not mentioned) by r262901
Fix the arm sys_sigreturn(): its argument is a struct ucontext, not a
struct sigframe containing the struct ucontext.

The signal trampoline return code on the other hand DOES have just a
struct sigframe on the stack to work with, so have it get a pointer to
the ucontext out of there to pass along to sys_sigreturn.

In other words, make everything work right whether sys_sigreturn is
invoked from the trampoline or from userland code calling sigreturn(2).

Submitted by:	Takashi Komatsu <komatsu.taka@jp.panasonic.com>
Reviewed by:	cognet