* require vote account to be exempt
* make stake account rent exempt
* add rent exempted system instruction
* use rent exemption instruction in vote and stake api
* use rent exempted account while creating executable account
* updating chacha golden hash as instruction data has changed
* rent will be initialized for genesis bank too
* Implement CreditOnlyLocks
* Update credit-only atomic on account load
* Update credit-only atomic after bank.freeze_lock; store credits if all credit-only lock references are dropped
* Commit credit-only credits on bank freeze
* Update core to CreditAccountLocks
* Impl credit-only in System Transfer
* Rework CreditAccountLocks, test, and fix bugs
* Review comments: Pass CreditAccountLocks by reference; Tighten up insert block
* Only store credits on completed slot
* Check balance in bench_exchange funding to ensure commit_credits has completed
* Add is_debitable info to KeyedAccount meta to pass into programs
* Reinstate CreditOnlyLocks check on lock_account
* Rework CreditAccountLocks to remove strong_count usage
* Add multi-threaded credit-only locks test
* Improve RwLocks usage
* Review comments: panic if bad things happen; tighter code
* Assert lock_accounts race does not happen
* Revert panic if bad things happen; not a bad thing
This will allow BankClient to spin up a thread to use the Bank.
It'll also ease the transaction from BankClient to ThinClient since
it won't let you depend on Bank.
Drawback, you the transition from Bank to BankClient will be harder
because the Bank methods are inaccessible.
