Fix RCN's disabled "test_start_of_month_statement" unit test

[mkazin]

NOTE: I started working on this a while back, see the rcn_fix branch, an attempt which seems to have failed:
https://github.com/mkazin/StatementRenamer/tree/rcn_fix

This is going to need some bounds-checking, which may or may not need to be applied to all extractors.
It may need a better definition of the statement dates.
Have fun!

From text_rcn.py:

# TODO: this fails because we're parsing the statement date,
# rather than the statement period. Problem is the statement
# period doesn't include a year, which means we need to grab
# it from the statement date (and handle edge cases- ick)
# Let's try checking the PDF/data again (for various versions
# of this statement format) to see if there's some kind of
# halfway elegant solution to this extractor.