As shown in http://mzl.la/1hkKgkE there is no property named
`handlers` in the TryStatement node, but one named `handler`.
Previously, a TypeError (cannot reach `[0]` of `M.handlers`) exception
was thrown when using `uglifyjs` with the `—acorn` switch.
returns an UglifyJS2 AST given a Mozilla AST. Still needs some work to do
(need to create specific nodes like AST_SymbolRef, AST_SymbolLambda
etc. instead of base AST_Symbol, in order for the mangler/compressor to work
properly)
