[Tests] check specific validation error in miner tests
[Tests] check specific validation error in miner tests

BOOST_CHECK_THROW merely checks that some std::runtime_error is
thrown, but not which one.

One example of how this could lead to a test passing when a developer
introduces a consensus bug: the test for the sigops limit assumes
that CreateNewBlock fails with bad-blk-sigops. However it can
also fail with bad-txns-vout-negative, e.g. if a naive developer lowers
BLOCKSUBSIDY to 1*COIN in the test.

BOOST_CHECK_EXCEPTION allows an additional predicate function. This
commit uses this for all exceptions that are checked for in
miner_tets.cpp:
* bad-blk-sigops
* bad-cb-multiple
* bad-txns-inputs-missingorspent
* block-validation-failed

An instance of the CheckRejectInvalid class (for a given validation string)
is passed to BOOST_CHECK_EXCEPTION.

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