procps automake defines restrict which means the binaries for procps
binaries compile. However external programs may not of defined
restrict which means they will not complie if they include files found
in /usr/include/proc.
Includes from libc6 use __restrict and if is good enough for
them, its good enough for us.
The function will convert a signal number string to a signal name, or
vice a verse. Return value is string, which is an function user is
expected to free after use.
Signed-off-by: Sami Kerola <kerolasa@iki.fi>