Fix #630: Boolean.booleanValue() does not fail on null.
Fix #632: Everything but null should be a java.lang.Object.
Fix #631: Values returned from JS interop should be asInstanceOf'ed.

Nothing guarantees that facade types are accurate, so a value
returned from a call to a facade type method should be
asInstanceOf'ed to ensure that it conforms to the expected type.
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Merge pull request #634 from alexander-myltsev/master

Update README.md
Merge pull request #633 from sjrd/typecheck-fixes

Several fixes to bugs discovered through the IR type checker
Rise checksizes limits a bit for the fixes to come.
Fix the IR type of array updates.
Fix the IR type of conversions to Byte/Short.
Add the type of `this` of Function nodes.

After all, it is part of their signature as much as the types
of their parameters.
Record ancestors of hijacked classes in IR.
Fix the mutable flag of VarRefs and Selects.
Fix some IR types with legit Casts.
Fix encoded name of Null and Nothing in signatures.
Fix the IR type of Object, Null and Nothing.
Fix the IR type of js.undefined.
Cancel opt of Function as js.Function if `this` is needed.
Fix IR type of reflective array update.
Fix IR types and correctness of Scala fun to JS fun.
Fix IR type of Array.clone().