library: allow duplicated results for <pids> interface

library: allow duplicated results for <pids> interface

Ok, here is that rather major internal redesign hinted
at in the three previous commits. Its need was quickly
revealed after adapting top then attempting to display
newly added 'CGNAME' fields and an existing 'CGROUPS'.

That very quickly generated a SEGV. And the reason was
just as quickly recognized. Both fields relied on that
proc_t.cgroup member yet whichever result structure is
first in a stack is the one which assumes ownership of
of the vectored sting by resetting its cgroup to NULL.

So this commit introduces reference counting for a few
of the fields in the proc_t. Specifically there are 17
entries in the Item_table dealing with strings/vectors
where ownership is transferred to newlib. Now whenever
such fields are represented more than once in a stack,
the strings will be duplicated instead of transferred.
In this way we can generally remain optimized avoiding
string copies, yet still accommodate them when needed.

There's an exception to this scheme: those true string
vectors (CGROUP_V, CMDLINE_V and ENVIRON_V). When such
fields are duplicated in a stack the result structures
beyond the first will be set to NULL, which the caller
will (should) already be equipped to deal with anyway.

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