Fix most compiler warnings

[cichli]

Gets us partway to #875. This is pretty weird though:

In cider-eval-buffer:
cider-interaction.el:1644:8:Warning: function cider-eval-buffer used to take
    0-1 arguments, now takes 0

cider-eval-buffer is defined here but is then aliased to cider-load-buffer here. The alias was added to fix #865 - I guess for now we should just delete cider-eval-buffer and keep the alias? If/when the source-tracking eval patch is merged to nREPL we can look into making the distinction between eval and load more clear, and have these as separate commands again.

The following warnings will require more significant restructuring of things, mostly handled by #1068:

In nrepl-make-response-handler:
nrepl-client.el:873:24:Warning: assignment to free variable `cider-buffer-ns'

In end of data:
nrepl-client.el:1442:1:Warning: the following functions are not known to be
    defined: cider-need-input, cider-current-repl-buffer,
    cider-repl-emit-output, cider-repl-emit-err-output,
    cider-repl-emit-interactive-err-output, cider--close-buffer,
    cider-popup-buffer-mode

In cider--version:
cider-util.el:151:12:Warning: reference to free variable `cider-version'

In end of data:
cider-repl.el:1106:1:Warning: the function `cider-version' is not known to be
    defined.

In end of data:
cider-mode.el:162:1:Warning: the following functions are not known to be
    defined: cider-macroexpand-1, cider-macroexpand-all, cider-inspect,
    cider-selector

In cider-ensure-op-supported:
cider-interaction.el:239:136:Warning: reference to free variable
    `cider-version'

In cider--check-required-nrepl-ops:
cider-interaction.el:248:24:Warning: reference to free variable
    `cider-version'

In cider--check-middleware-compatibility-callback:
cider-interaction.el:291:47:Warning: reference to free variable
    `cider-version'

In end of data:
cider-interaction.el:2151:1:Warning: the function `cider-jack-in' is not known
    to be defined.

In end of data:
cider-doc.el:394:1:Warning: the following functions are not known to be
    defined: cider-apropos, cider-apropos-documentation, cider-grimoire,
    cider-grimoire-web, cider-grimoire-lookup, cider-grimoire-web-lookup

[bbatsov]

cider-eval-buffer is defined here but is then aliased to cider-load-buffer here. The alias was added to fix #865 - I guess for now we should just delete cider-eval-buffer and keep the alias?

Yep. How I missed this is beyond me. I'll do that update myself.

[bbatsov]

👍 Great work! Now it's time for the big fun cider-interaction split.

[cichli]

btw, do you know what causes all of the Cannot open load file: clojure-mode errors on Travis? They seem to obscure any other compiler warnings.

[bbatsov]

Most likely it's cask. //cc @lunaryorn

[swsnr]

@bbatsov I'm not sure what I'm supposed to say here… Cask doesn't compile, and if I'm to take a look at these warnings, I'd at least like to see them somewhere.