crypto/x509: Parse Extended Key Usage extension
crypto/x509: Parse Extended Key Usage extension

This changeset makes it possible for crypto/x509 to parse
certificates that include the 'Extended Key Usage' extension
with the critical bit set.

R=agl1
CC=golang-dev
http://codereview.appspot.com/4277075

Committer: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>

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