Make clojure-mode.el pass checkdoc.

New docstrings for:
clojure-font-lock-syntactic-face-function
put-clojure-indent
define-clojure-indent
add-custom-clojure-indents

Improved doc-strings for:
clojure-fill-paragraph
clojure-backtracing-indent
clojure-indent-function.

Related touch-ups.