library: final tweaks to code and/or comments, 3rd gen

library: final tweaks to code and/or comments, 3rd gen

With the dust now settling on all those 3rd generation
upgrades, this patch tries to provide some consistency
among the separate modules involved. Someday we should
consider a 4th generation where all redundant code has
been removed and isolated in a new shared source file.

Following is a summary of significant changes (if any)
to each of these now upgraded 3rd gen library modules.

<meminfo> ............................................
. strictly formatting/comment changes, code unaffected

<pids> ...............................................
. replaced a local mkSTR macro with existing STRINGIFY
. added fetch narrative explaining duplicate addresses

<slabinfo> ...........................................
. rearranged some free logic for procps_slabinfo_unref
. added fetch narrative explaining duplicate addresses

<stat> ...............................................
. added #define ENFORCE_LOGICAL, just as in <slabinfo>
. replaced a local mkSTR macro with existing STRINGIFY
. alphabetized the function declarations in the header

<vmstat> .............................................
. made one coverity concession with read_vmstat_failed

[ several of these changes may reflect this author's ]
[ continuing pursuit of an unreasonable goal -- that ]
[ of a 'perfect' (plus 'pretty') C language program! ]

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