library: repair <pids> api boo-boo in the 'select' i/f

The patch referenced below corrected some flaws in the
procps_pids_select implementation. But, there remained
one flaw which this commit will now hopefully address.

Rather than assume callers wished to select only tasks
and not threads meant a command like 'top -H -p 10329'
works differently under newlib than release 3.3.17. It
fails to honor the '-H' (threads) switch under newlib.

So, to fix that oops, we'll allow that select function
to get threads or tasks depending on its 'which' parm.

Reference(s):
. Oct 2015, some flaws corrected
commit bc616b3615

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

proc/pids.h

@@ -189,8 +189,10 @@ enum pids_fetch_type {
 };
 
 enum pids_select_type {
-    PIDS_SELECT_PID  = 0x10000,
-    PIDS_SELECT_UID  = 0x20000
+    PIDS_SELECT_PID         = 0x10000,
+    PIDS_SELECT_PID_THREADS = 0x10001,
+    PIDS_SELECT_UID         = 0x20000,
+    PIDS_SELECT_UID_THREADS = 0x20001
 };
 
 enum pids_sort_order {