Clarify purpose of "project number" field.

[GoogleCodeExporter]

Right now, the hovertext for the "project number" field when creating a new 
project says this: "should be very short; doesn't have to be a number, probably 
shouldn't have spaces". Additionally, in the DB it's a VARCHAR(30). We should 
look at where it's used and clarify or remove the input.

Original issue reported on code.google.com by rws...@gmail.com on 19 Jan 2012 at 2:03