This commit addes a couple of tests to ensure performing math operations
on a 5-byte integer, even if the result is a 4-byte integer, is considered
invalid.
Both the script tests (positive and negative) and tx texts (ditto) are
present. Some of the tx tests in the negative section have been
replaced by a comment line explaining why that test is elided, to add in
diffing. The reasons were always that they test things handled by other
parts of the btcd stack (normally chain). For example MAX_MONEY, number
of outputs, coinbase sizes etc.
Much of the inital test logic from @dajohi using hand transcribed tables
for selected tests. The json parsers, script format parser and a lot of
cleaning up/bugfixing from your truly. @davecgh had some input too.
