Add temperature compensation

A new tempcomp directive can be used to specify a file for reading
current temperature, update interval and compensation coefficients. The
clock frequency corrections are applied in local module and are invisible
in upper layers. The measurements and corrections can be logged to
tempcomp.log file.

local.h

@@ -188,4 +188,9 @@ extern int LCL_MakeStep(double threshold);
    and zero cancels scheduled leap second. */
 extern void LCL_SetLeap(int leap);
 
+/* Routine to set a frequency correction (in ppm) that should be applied
+   to local clock to compensate for temperature changes.  A positive
+   argument means that the clock frequency should be increased. */
+extern void LCL_SetTempComp(double comp);
+
 #endif /* GOT_LOCAL_H */