needed changes in process_model for resend data

in pushing data by .csv to emoncms i had to change some behaviors in process_model.php

In process_model is a security check to not calculate values for a input older then 2 Hours. 
This check is in Power_to_kwh, Power_to_kwhd, histogram and input_ontime.

By re feeding emoncms with older data, maybe from the energy company over a full year, this values have to get passed. maybe this can be done by setting a global variable or a variable by user for that. 

by this checks i found a behavior error in histogram, cause values ware accumulated at same timestamp.
This is wrong in my opinion, cause a timestamp is unique for a feed.

This has to be changed in the else part in histogram.

// wrong, cause time is uniqe, don't accumulate data !!!
// $new_kwh = $last_kwh + $kwh_inc;
   $new_kwh = $kwh_inc;

I would do this by myself, but maybe someone can tell me how to work with pull requests.

Thanks Marc