#28 account names can clobber

[Anonymous]

When adding a new account, the name is not checked.
This can allow a user to create an account with an
existing account's name and see the details of that
account.

It also messes up the tables; now each user with that
account name sees two copies.

bug found in 0.4.0

To duplicate bug:
1.as admin create two users: user1 and user2, give each
of them rights to add/edit/remove accounts and
transactions.

2.login as user1.

3.create a new account "test account", set it's opening
balance to $100.

4.add a transaction "secret transaction", with a $10 debit.

5.logout and login as user2.

3.create a new account "test account", set it's opening
balance to $250.

4.view the account. You will see it has $340 in it; an
opening balance, the secret transaction, and another
opening balance.