Add a way to edit a pledge

This just lets you change the quantity.
Attempt to robustify tests

Some of these tests were failing intermittently (rarely) with an error
like:

<Thu, 18 Apr 2013 15:31:03 PDT -07:00> (256995000[ns]) expected but was
<Thu, 18 Apr 2013 15:31:03 PDT -07:00> (256994000[ns]).

I.e., off by 1 microsecond. Unclear what was causing this but I suspect
some rounding on save. So, now I grab the time after save in order to
compare it to the later value.