Don't mutilate keyword arguments in :bind

Don't mutilate keyword arguments in :bind

The parsing logic in `use-package-normalize-pairs' is not designed to
deal with keyword arguments. However, `use-package-normalize-pairs' is
used to process the arguments to :bind, which can include keyword
arguments. These keyword arguments are supposed to be passed untouched
to the underlying `bind-keys' function, but there is a clause in
`use-package-normalize-pairs' that replaces lists with their first
element. Thus an invocation like:

(use-package company
  :bind (:map company-active-map
         :filter (company-explicit-action-p)
         ("RET" . company-complete-selection)))

Generates code like this:

(bind-keys
  :map company-active-map
  :filter company-explicit-action-p
  ("RET" . company-complete-selection))

Which generates an error since `company-explicit-action-p' is now
being referenced as a variable rather than a function.

The proper solution is to refactor the logic that goes into parsing
uses of :bind, but this commit adds a temporary patch to eliminate the
above problem, while trying to be as reverse-compatible as possible.
In particular it just inhibits the list-to-first-element
transformation when the previous element processed was a keyword.