- move these optimisations out from `Compressor` to `OutputStream`
- fixes behaviour inconsistency when running uglified code from global or module levels due to redefinition
The following is wrong:
`a == (b ? a : c)` => `b`
Because:
- `b` may not be boolean
- `a` might have side effects
- `a == a` is not always `true` (think `NaN`)
- `a == c` is not always `false`
- remove call to evaluate() in is_constant() and let nested optimize() does its job instead
- reject RegExp in is_constant() and remove special case logic under collapse_vars
- operands to conditionals optimisation are now always evaluate()-ed
- throw error in constant_value() instead of returning undefined to catch possible bugs, similar to make_node_from_constant()
- optimise binary boolean operators under `evaluate` instead of `conditionals`
In 992b6b9fcc unit test broke (which I missed). This was due to undeclared variables not being side-effects free.
However, since they're really not side-effect free, just declare them in the test cases.
- do multiple passes in tighten_body if it was changed
- transform if (foo) return x; return y; ==> return foo?x:y
- don't optimize !0 as true (use best_of after evaluation of constant expr)
With hoist_vars off we now beat UglifyJS v1 on jQuery-1.8.1
