/*
 * call-seq:
 *    ProcTable.ps(pid=nil)
 *    ProcTable.ps(pid=nil){ |ps| ... }
 *
 * In block form, yields a ProcTableStruct for each process entry that you
 * have rights to.  This method returns an array of ProcTableStruct's in
 * non-block form.
 *
 * If a +pid+ is provided, then only a single ProcTableStruct is yielded or
 * returned, or nil if no process information is found for that +pid+.
 */
static VALUE pt_ps(int argc, VALUE* argv, VALUE klass){