libpcp: add missing pthread_mutex_destroy calls for pc_lock (pmcd ipc lock)
libpcp: add missing pthread_mutex_destroy calls for pc_lock (pmcd ipc lock)

Original patch by Markiyan Kushnir <markiyan.kushnir@gmail.com>
to address https://github.com/performancecopilot/pcp/issues/62.

Some refactroring to "downgrade" the name of the new static function
involved (and on reflection some of their peers in context.c) from
__pmFooBar() to foobar() as these symbols are not, and never will be,
visible at the library API (cosmetic and code readability issue).

adfernandes/pcp,wuliming/pcp,wuliming/pcp,wuliming/pcp,adfernandes/pcp,wuliming/pcp,adfernandes/pcp,wuliming/pcp,adfernandes/pcp,wuliming/pcp,adfernandes/pcp,wuliming/pcp,adfernandes/pcp,adfernandes/pcp,wuliming/pcp,adfernandes/pcp