libpcp: fix __pmStringValue() to allow negative PM_TYPE_FLOAT values
libpcp: fix __pmStringValue() to allow negative PM_TYPE_FLOAT values

Check for float to double truncation was wrong.

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