[Fix #426] Expose variable to ignore paths in the middleware

[expez]

This makes it possible to easily exclude certain files and directories
for analysis.

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The code for this already exists in the middleware. Not sure why a setting was never created. Perhaps we just forgot?

[expez]

@bbatsov While I'm in here, any idea about how to fix the build?

[bbatsov]

@expez I see that the build is failing because CIDER's master now depends on Emacs 25.1 (as sesman, the new connection management library depends on it). I guess you'll have to update the build matrix.

[bbatsov]

clj-refactor.el:289:1:Error: defcustom for ‘cljr-middleware-ignore-paths’ fails to specify containing group

That fails because the group of the defcustom is not specified. I guess you didn't configure the top-level group to just infer that everything starting with cljr should go to the same group.

[bbatsov]

I wonder if ignored-paths won't be a better name for this, as normally I'd assume something named ignore-paths means something else.

[expez]

@bbatsov I renamed the variable in clj-refactor, but the variable name in the backend was already commited to when we released 2.3.1.

[expez]

Merged manually