[ADDED] getrealbalance wrapper for payouts

During payouts, we must ensure our wallets main accounts has the funds
to payout users. Hence we implement a wrapper method:

* If account count == 1 we only have main account, return getbalance
* Else return our main accounts balance - calculated unconfirmed

This should keep getbalance untouched when used on other places but
gives our payout processing a proper main account balance.

It's mostly a wrapper for those wallets running multiple accounts in one
wallet. They are warned on the front-end already but this ensure payouts
process properly.

Fixes #1755 once merged.
Update bitcoinwrapper.class.php
[FIX] fix for negative balance

using php abs() should do the trick with negative balance
[UPDATE] Return negative balance if main is negative
Merge pull request #1757 from MPOS/getrealbalance-wrapper

[ADDED] getrealbalance wrapper for payouts