libcpp: __pmAddOptArchive(), __pmAddOptArchiveList()
libcpp: __pmAddOptArchive(), __pmAddOptArchiveList()

Extend these to allow multiple archives to be specified when
PM_OPTFLAG_MULTI is not set.

- The semantics for when PM_OPTFLAG_MULTI is set are retained. A
  list of archives to be used with multiple contexts is created.
  See pmstat(1) for an example.

- When PM_OPTFLAG_MULTI is not set, then the list of archives
  is accumulated as a comma-separated list which will be passed
  to pmNewContext(3) in order to create a single context containing
  multiple archives.

- Single archive semantics are preserved with these changes.

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