Introduce the option to hide special buffers

Some "boring" buffers can now optionally be hidden by
the users via the use of the `nrepl-hide-special-buffers` setting.
By default all special buffers are visible.
Fix nrepl-hide-special-buffers docstring.
Fix test names.
Merge pull request #255 from bbatsov/hide-bufffers

Introduce the option to hide special buffers
Improve compilation error handling

To avoid delays associated with retrieval of the stacktrace, highlighting is
based on the exception message that is reported by the stderr-handler in
nrepl-load-file-handler.  The exception trace is put in the *nrepl-error*
buffer, but not displayed by default.

Adds an nrepl-visit-error-buffer function, to visit *nrepl-error*.

Installs nrepl-jump-to-compilation-error as the next-error-function in
nrepl-interaction-mode buffers, to jump to the compilation error using
next-error.

Adds an optional eval-error-handler to nrepl-make-response-handler.

Adds nrepl-popup-on-error, to control whether stacktraces (globally) are popped
up by default.