Incorrect sigaction output for MIPS

[Chris Dearman]

The following patchset adds a simple self-verifying test for
sigaction output (which currently fails on MIPS) and a change to
signal.c to fix the saigaction output.

Without this change the output is garbled on MIPS eg:
rt_sigaction(SIGUSR2, {0x10000000, [RT_69 RT_70 RT_71 RT_72 RT_73 RT_75 RT_87], SA_NOCLDSTOP}, {SIG_DFL, ~[HUP INT 

The correct output after applying the patch:
rt_sigaction(SIGUSR2, {SIG_IGN, [HUP INT], SA_RESTART}, {SIG_DFL, [], 0}, 16) = 0

Chris