Julia 0.2 compatibility

As discussed in shashi/Interact.jl#6, I'd like to overload `lift` from PyPlot in order to allow interactive plots, but making PyPlot require React would currently mean breaking compatibility with Julia 0.2, which I'd like to keep for a while.

Fortunately, with a couple of trivial patches to React, it can be made compatible with Julia 0.2.

(This leads to a couple of harmless warnings when running the test suite, due to the use of a deprecated form of `@test_throws`, but this doesn't seem like a big deal to me.  Most users won't run the test suite anyway.)