Log accepted blocks via submitblock.

ok @davecgh
Implement BIP0061 reject handling (pver 70002).

This commit implements reject handling as defined by BIP0061 and bumps the
maximum supported protocol version to 70002 accordingly.

As a part of supporting this a new error type named RuleError has been
introduced which encapsulates and underlying error which could be one of
the existing TxRuleError or btcchain.RuleError types.

This allows a single high level type assertion to be used to determine if
the block or transaction was rejected due to a rule error or due to an
unexpected error.  Meanwhile, an appropriate reject error can be created
from the error by pulling the underlying error out and using it.

Also, a check for minimum protocol version of 209 has been added.

Closes #133.
IMPORT PATH MODIFICATION CHANGESET
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Please use this changeset as the first one on top of the conformal codebase.
Note that if there are new imports, they need to be changed as part of this
changeset. In general, use "git rebase" on github.com/conformal's version
and apply this changeset first.