library: add sequential access to that pids collection

To ease the transition to the new interface, for other
than that top program, individual read provisions have
been added to the <proc/pids.h> API. This represents a
refinement of a position stated in a post noted below.

Reference(s):
http://www.freelists.org/post/procps/newlib-ps-fix

Signed-off-by: Jim Warner <james.warner@comcast.net>

proc/libprocps.sym

@@ -43,6 +43,9 @@ global:
 	procps_meminfo_stack_fill;
 	procps_meminfo_stack_alloc;
 	procps_pids_new;
+	procps_pids_read_next;
+	procps_pids_read_open;
+	procps_pids_read_shut;
 	procps_pids_reap;
 	procps_pids_ref;
 	procps_pids_reset;