Bug 886104 - Remove assert in ParCallToUncompiledScript. (r=nmatsakis)
Bug 886144 - Remove incorrect inlining of ThrowError. (r=nmatsakis)
Bug 877893 - Part 1: Convert string VM functions needed for concatenation to take ThreadSafeContext. (r=billm)
Bug 877893 - Part 2: Support string concat in parallel in Ion. (r=djvj)
Bug 877893 - Part 3: VM & Ion changes to make MToString threadsafe. (r=billm)
Bug 877893 - Part 4: Make MToString support doubles and threadsafe. (r=djvj)