library: accumulated changes to <pids> code & comments

library: accumulated changes to <pids> code & comments

A patch containing the following miscellaneous tweaks:

. avoided distortions unique to PROCPS_PIDS_TICS_DELTA
. addressed several smatch warnings and/or suggestions
. ensured oldproc_close invoked should tally_proc fail
. keeping that namespace clean, added a missing #undef
. added 2 comments acknowledging pids_item as unsigned
. added/clarified comments regarding proc flags & strv

From smatch analysis:
. these were indeed boo-boos
pids.c:580 make_hist() warn: the 'Hr' macro might need parens
pids.c:1058 procps_pids_reap() warn: variable dereferenced before check 'info' (see line 1056)
. these were not errors (and we did double check)
pids.c:1067 procps_pids_reap() warn: double check that we're allocating correct size: 8 vs 128
pids.c:1068 procps_pids_reap() warn: double check that we're allocating correct size: 8 vs 128

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