Bug 1046964 - Warn when encountering a string expression statement, that would be a directive but isn't in the right position, when respecting the non-directive would change semantics.  r=njn

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extra : rebase_source : ee36adb345a500633815c5bfe3f6f2dd354ded87
Bug 894653 - Self-host Error.prototype.toString, and fix an edge-case bug in the current implementation.  r=till

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extra : rebase_source : 5e80c2021071d11ef44209d371a38ed3be2a9178