Serious bug fix: while interval duration SHOULD be computed by using

previous data point (i.e., q->secs - p->secs), the duration to multiply
the wattage value by SHOULD NOT be.  Instead, should multiply by
rec_int.  (My ride from Jul 31, 2007 demonstrates the problem.  I
started an interval with a 1-sec wattage of 773 after a ~48 second rest.
Using the old code, that gets credited as 773 watts for 48 secs!)

src/cpint/cpint.cpp

@@ -200,7 +200,7 @@ update_cpi_file(cpi_file_info *info,
                     goto done;
                 }
             }
-            sum += (q->secs - prev_secs) * q->watts;
+            sum += data.rec_int_ms / 1000.0 * q->watts;
             double dur_secs = q->secs - p->secs;
             double avg = sum / dur_secs;
             int dur_secs_top = (int) floor(dur_secs);