WIP message - Fix a bunch of "method redefined" warnings

These come in pairs like
* "warning: method redefined; discarding old config_files"
* "warning: previous definition of config_files was here"

In one case, I changed the code to alias the old method first, so it
isn't discarded when its original name is reused. This is straight
outta Compto^H^H^HRails' around-advice pattern, #alias_method_chain.
The rest look like mistaken duplicate definitions, e.g. using
attr_accessor for an instance variable that already has a reader.

squash! Fix a bunch of "method redefined" warnings
Rename block params to fix "shadowing outer local variable" warnings
Fix a few "assigned but unused variable" warnings

Note that "_" is the official magic name to use when you're
intentionally abandoning an assignment (typical use case, seen here:
unneeded elements being discarded in a parallel assignment) because
Ruby supresses the warning for that name.

In Ruby 2.0, you can prefix a variable name with an underscore to get
the same behavior -- without sacrificing the documentation-value of
naming things.
Fix warnings about uninitialized instance variables
Add whitespace to fix ambiguous operator precedence

It said: "warning: `+' after local variable is interpreted as binary
operator even though it seems like unary operator."
Enable warnings when running the tests
Rake is a development dependency
Add a quick Gemfile so you can install test deps with Bundler

(I'm trying to figure out how to install rip -- its website with the
standalone installation instructions is gone now... but it seems like
switching to Bundler + gemspec would be reasonable at this point?)

[20 min later] ... yeah, this isn't going well. I'm going to remove
deps.rip. RIP rip.
Fix a ton of 'void context' warnings for free by just using better matchers
WIP message -  fix the rest of the warnings
Fix "./lib/hirb/version.rb:2: warning: already initialized constant VERSION "