libpcp __pmNotifyErr: correct va_list usage
libpcp __pmNotifyErr: correct va_list usage

In the do_syslog case, a va_list parameter was being passed to
snprintf, and never reset for subsequent use by vpmprintf().
Use the correct varargs operations.

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