Add a separate pmda indom lookup routine for names (vs cached data)
Add a separate pmda indom lookup routine for names (vs cached data)

Found a need for this while developing pmdagluster which stores data
in the indom caches (needing one inst-based lookup) as well as using
a reverse instance-to-name lookup for its store callback.

andyvand/cygpcpfans,wuliming/pcp,prasincs/pcp,adfernandes/pcp,tjanez/pcp,mbaldessari/pcp,tjanez/pcp,andyvand/cygpcpfans,aeg-aeg/pcpfans,wuliming/pcp,edwardt/pcp,tjanez/pcp,aeg-aeg/pcpfans,prasincs/pcp,tjanez/pcp,adfernandes/pcp,aeg-aeg/pcpfans,tjanez/pcp,andyvand/cygpcpfans,prasincs/pcp,wuliming/pcp,andyvand/cygpcpfans,tjanez/pcp,aeg-aeg/pcpfans,edwardt/pcp,edwardt/pcp,tjanez/pcp,mbaldessari/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,prasincs/pcp,adfernandes/pcp,andyvand/cygpcpfans,wuliming/pcp,wuliming/pcp,aeg-aeg/pcpfans,andyvand/cygpcpfans,andyvand/cygpcpfans,aeg-aeg/pcpfans,aeg-aeg/pcpfans,wuliming/pcp,mbaldessari/pcp,mbaldessari/pcp,prasincs/pcp,edwardt/pcp,wuliming/pcp,prasincs/pcp,edwardt/pcp,aeg-aeg/pcpfans,tjanez/pcp,prasincs/pcp,adfernandes/pcp,mbaldessari/pcp,wuliming/pcp,adfernandes/pcp,edwardt/pcp,prasincs/pcp,andyvand/cygpcpfans,mbaldessari/pcp,edwardt/pcp,edwardt/pcp