Re-enable repeated firing of confirmation events

[cgewecke]

At the moment when a transaction receipt is immediately available after a method call, the confirmation event only fires once. It seems like the subscription logic for this case might have been accidentally disabled while making web3-core-method compatible with Parity's instant-seal. This issue primarily affects testing clients like ganache but possibly also Parity and Geth in dev mode.

Because startWatching is set on a delay here and only if the promise hasn't resolved, the subscription never initiates and repeated firings of the confirmation handler never happen.

This PR tries to re-enable multiple confirmations by

• removing the promise condition and delay
• passing the immediately retrieved receipt to checkConfirmation so it can be emitted
• adding logic to handle the case where the direct call to checkConfirmation required by instant-seal is doubled by a call made by the startWatching method.
• adding a test for multiple confirmations.

[coveralls]

Coverage increased (+0.07%) to 85.907% when pulling 522d54a on cgewecke:fix/repeat-confirmations into c9ca65d on ethereum:1.0.

[coveralls]

Coverage increased (+0.07%) to 85.907% when pulling 522d54a on cgewecke:fix/repeat-confirmations into c9ca65d on ethereum:1.0.

[coveralls]

Coverage increased (+0.07%) to 85.875% when pulling b5e5099 on cgewecke:fix/repeat-confirmations into 54daf21 on ethereum:1.0.

[coveralls]

Coverage increased (+0.07%) to 85.907% when pulling 522d54a on cgewecke:fix/repeat-confirmations into c9ca65d on ethereum:1.0.

[frozeman]

Thanks for the find!

[cgewecke]

Thanks :)