Addressed corner case in Firefox repository.

Some commits have Author = "%aN", Date = "   "  and Committer = "%cN".

We throw away these commits, since no date is available...
We could try harder, and interpolate the date value using the dates
of the previous and the following commits.
Starting to generate GNUPlot diagrams.

Scripting them all, to make them reproducible and documented.
Now generating plots of LOC vs Contributors.
Merge branch 'GitStatistics'