bug#19711: 25.0.50; (ad-is-adviced sym) is inconsistent with (advice--p (advice--symbol-function sym))

[Oleh Krehel]

`ad-is-adviced' expands to:

    (get 'foo 'ad-advice-info)

This code will not detect if the function `foo' is being instrumented
with `elp-instrument-package' (which is a form of advice).

On the other hand, this code from `advice-remove' will work:

    (advice--p (advice--symbol-function 'foo))

To summarize, functions instrumented by elp aren't recognized as adviced
by `ad-is-advised', even though :around advice: even shows up in the
docstring.

A fix could be to change `ad-is-adviced' to expand to either

    (or (get 'foo 'ad-advice-info)
        (get 'foo 'elp-info))

or

    (advice--p (advice--symbol-function 'foo))