Infer types for method references

[Chuck]

Types for method references are not inferred. For example:

x = X()
m = ref x.bar
# error: Cannot infer type for "m" because
# the type of the right hand expression is unknown.

Cobra should infer the type. A search for a compatible type sig should start in the current box and proceed out to the declared and used namespaces. If no match is found, a private, generated method sig should be created.