Made the sendmany command accept "*" as the account name to send from all accounts.

Without this change sendmany requires a specific account to send coins
from. So we cannot send coins the same way "sendtoaddress" and the GUI
do. The latter actually send coin from the "" account but when they check
the balance they get the whole wallet balance, not only the "" balance.
This commit implements the same behavior in the sendmany command when
the account name "*" is provided.
Merge pull request #74 from sigmike/sendmany_from_all_accounts

sendmany from all accounts