Use 'low S' as malleability breaker rather than 'even S'

[sipa]

As we don't have any releases enforcing this yet, and no others that have picked it up, we can change this without harm. It has the advantage of on average decreasing signatures by 0.5 byte, and avoiding DER padding problems.

[gmaxwell]

Pieter and I had discussed this a few weeks ago before his vacation.

ACK code, also, I ran 30,000 signatures through this and confirmed that the average signature size is reduced by 0.5 byte, the maximum is reduced by 1 byte, and all 30,000 resulting signatures validated.

[gavinandresen]

ACK

[gavinandresen]

Ignore pull-tester errors for now, I'm debugging it...

[BitcoinPullTester]

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