Using a built-in module name as a type causes an internal error

[jpolitz]

For example:

a :: option<Number> = some(5)

which is an easy typo of the intended program:

a :: Option<Number> = some(5)

[jpolitz]

NB: This is a namespace error, not a type-checker error

[blerner]

Well it's slightly less bad on the modules branch: "Name not found in globals.types: option"

Still not good, but at least the internal error is avoided