How long ago was this? The Rules

Each submission must be a full program.

The program must take input as two comma-separated dates in the form YYYY-MM-DD, and print the number of days that has passed since the second date to STDOUT as if today was the first date (if the second date would be in the future, output a negative number) plus an optional trailing newline, and nothing else. Assume both dates are in the Gregorian calendar.

The program must not write anything to STDERR.
Note that there must be an interpreter so the submission can be tested.

Submissions are scored in bytes, in an appropriate (pre-existing) encoding, usually (but not necessarily) UTF-8. Some languages, like Folders, are a bit tricky to score - if in doubt, please ask on Meta.

This is code-golf, so shortest code wins


Examples
Input:
2015-12-03,2015-12-01
Output:
2
Input:
2015-12-03,2014-12-01
Output:
367
Input:
2015-12-03,2013-12-03
Output:
730
Bash + GNU utilities, 37



tr , \\n|date -f- +%s|dc -e??-86400/p


tr replaces the comma with a newline.  date reads the newline separated dates and outputs the number of seconds since the Unix epoch that the passed-in date represents.  These numbers are then put on the dc stack.  Then its a simple matter of subtraction and divide by (24*60*60).  In this case, dc stack-based RPN arithmetic evaluation is better than bc or bash $( ), mostly because the subraction-before-division needs no parentheses.

Input via STDIN:

$ echo 2015-12-3,2015-12-1 | ./longago.sh
2
$ echo 2015-12-3,2014-12-1 | ./longago.sh
367
$ echo 2015-12-3,2013-12-3 | ./longago.sh
730
$