Require strictly-standard encodings in mempool

[sipa]

This will make the mempool require strictly DER-encoded signatures, and restrict public keys to being either compressed or uncompressed (so no "hybrid" ones).

See the discussion here: http://comments.gmane.org/gmane.comp.bitcoin.devel/1973

[BitcoinPullTester]

Automatic sanity-testing: PASSED, see http://jenkins.bluematt.me/pull-tester/20d0810f300fdcb6a0af6cb310c4702cdd956009 for binaries and test log.
This test script verifies pulls every time they are updated. It, however, dies sometimes and fails to test properly. If you are waiting on a test, please check timestamps to verify that the test.log is moving at http://jenkins.bluematt.me/pull-tester/current/
Contact BlueMatt on freenode if something looks broken.

[jgarzik]

ACK

[laanwj]

ACK

[petertodd]

ACK

One reason I'd love to see canonical encodings mandated sooner rather than later is because they are going to make it a lot harder to write software for some of the really stripped down secure hardware stuff I'd like to see happen eventually. Many of these environments are downright anemic, smartcards for instance, so any fixed dependencies are a big problem.