library: ensure thread group leader retrieval accuracy

library: ensure thread group leader retrieval accuracy

With that recent addition of the autogroup provisions,
it became apparent that '/proc/<pid>/task' information
is sometimes incomplete. In fact, there's no autogroup
file at all in any '/proc/<pid>/task/<pid>' directory!

As a result, when the top -H mode was invoked, all the
processes showed a -1 for AGID, even the group leader.

So, this commit will ensure that for every TGID leader
its basic '/proc/<pid>' directory will always be used.
The 'task' subdirectory is now only used for siblings.

[ and it's time that readeither prologue was updated ]

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