Fix memory leak reiniting PMDA hash table for dynamic metrics
Fix memory leak reiniting PMDA hash table for dynamic metrics

Test qa/957 picked up on a memory leak in the handling of the
metric table hash lookup optimization, where second/subsequent
calls to pmdaRehash would rewrite the hash table, accidentally
leaking any entries written to it earlier.

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