Add missing require for pkg-info

Caused the following byte-compilation warning:


nrepl.el:3387:1:Warning: the function `pkg-info-format-version' is not known to be defined.
Add `nrepl-switch-to-relevant-repl-buffer' as separate functionality.

Commit 12558e8 breaks `nrepl-switch-to-repl-buffer' functionality by
assuming that all nrepl connections will be made using
`nrepl-jack-in'.

This commit reverts to old `nrepl-switch-to-repl-buffer'. A new
function `nrepl-switch-to-relevant-repl-buffer' is added as a
convenience function to switch to the correct nrepl buffer from a
given clojure buffer.
Extract banner generation to a separate function
Add missing pkg-info dep to Cask
Replace some cl-lib functions with dash equivalents
Don't attempt el-doc without a session

When there is no session available, and eldoc was activated, there
would be an error message reported by eldoc complaining of a wrong
type.  The error was being caused by there being no tooling session.
Bump dash.el dep to 2.1.0
Fix library version discovery
Leverage function from dash 2.1 -elem-index
Fix next-error

Broken by nrepl-extract-error-info not returning the message as the
note.  This change also uses nrepl-note-p to locate notes, rather than
nrepl-note.
name of connection buffer uses project name and is not duplicated