derived metrics - remove bind-time messages
derived metrics - remove bind-time messages

Moved messages at bind-time (most usually when a new context is created)
from unconditional via pmprintf() to debug diagnostics guarded by
-D derive.  These messages, while informative, are not needed if the
application never uses the derived metrics with errors associated with
operand metrics being unavailable.

The change is most relevant to PCP archives, and in particular record
mode for pmchart.

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