Fix indexing of module functions that return enumeration types.

Fix indexing of module functions that return enumeration types.

Return types that consist of more than one word need to be enclosed in
braces, see Info node `(texinfo) Typed Functions'.  Otherwise they are
indexed incorrectly.

* doc/lispref/internals.texi (Module Misc, Module Nonlocal): Enclose
multi-word return types in braces.