Add test for ratio of increase in delay to stddev

Require that the ratio of the increase in delay from the minimum one in
the stats data register to the standard deviation of the offsets in the
register is less than maxdelaydevratio or the difference between
measured offset and predicted offset is larger than the increase in
delay. In the allowed delay increase is included also skew and maximum
clock frequency error.

maxdelaydevratio is 10.0 by default.

cmdparse.h

@@ -42,6 +42,7 @@ typedef enum {
   CPS_BadMinpoll,
   CPS_BadMaxpoll,
   CPS_BadPresend,
+  CPS_BadMaxdelaydevratio,
   CPS_BadMaxdelayratio,
   CPS_BadMaxdelay,
   CPS_BadKey,