The removeprunedfunds() RPC was returning misleading or incorrect error
codes (for example RPC_INTERNAL_ERROR when the transaction was
not found in the wallet). This commit fixes those error codes:
- RPC_INTERNAL_ERROR should not be returned for application-level
errors, only for genuine internal errors such as corrupted data.
This error code has been replaced with RPC_WALLET_ERROR.
This commit also updates the test cases to explicitly test the error code.
This commit fixes the module-level docstrings for the tests and helper
modules in qa. Many of these tests were uncommented previously - this
commit ensures that every test case has at least a minimum level of
commenting.
