Add `ledger-read-date' - Read date & default to today.
`ledger-insert-effective-date': use `ledger-read-date'.

Running `ledger-insert-effective-date' will now prompt for a date with
a pre-filled value of the `(ledger-year-and-month)' ("2014/01/"). Just
pressing RET without inserting the 'day'-portion will insert the date
of today.
ledger-reconcile: Add option to insert an effective date when clearing transactions.
`ledger-read-date': Use `ledger-minibuffer-history'.
Use `ledger-read-date' where applicable.
Merge pull request #228 from the-kenny/emacs-prompt-effective-date

Emacs: Improve effictive-date-handling
Commodity column in default CSV format should match the displayed amount

If one uses --exchange to force CSV display amounts into a particular
currency, then the commodity output column should match that currency.

Without this patch, the commodity column contains the original
commodity, not the commodity for the exported amount.
Merge pull request #230 from purcell/fix-csv-commodity-column

Commodity column in default CSV format should match the displayed amount
Backed out recent changes that broke the complete cycling behavior.
ledger-mode: only modify completion-at-point-functions locally

Without this patch, the addition of pcomplete-completions-at-point
leaks into the global value of completion-at-point-functions.

See #227