Take feature namespace into account while building summary (fixes #1286)

Take feature namespace into account while building summary (fixes #1286)

Here's an attempt at a table to cover the different cases:

Feature
    Old (must be in features table)
        Continue
    Namespaced (might be stray value)
        In features table: Check that Crate dependency is in the list
        -> Non-optional dependency: Bail [PREVIOUSLY: bailed for non-optional dependency]
        -> Optional dependency: Insert feature of this name
        -> Else: Bail [PREVIOUSLY: bailed for unknown dependency or feature]

Crate
    Old (might be stray value)
        Non-optional dependency: Bail
        No dependency found: Bail
    Namespaced
        Non-optional dependency: Bail
        No dependency found: Bail

CrateFeature
    Old
        No dependency found: Bail
    Namespaced
        No dependency found: Bail