Retire vendored cacycle_diff.js for a diff-lcs-based diff view

Revisions#diff now computes an inline or side-by-side word diff
server-side (Page#diff_against, lib/html_word_diff.rb) instead of
shipping raw/escaped content to the browser for a 2008-era vendored
JS differ to mangle. View mode is picked via a `view` param, settable
either on the diff page itself or directly from the revisions#index
sticky bar next to "Diff revisions".

Also fixes a pre-existing bug in RevisionsController#diff's single-
revision branch, which set params[:start]/params[:end] instead of
params[:start_revision]/params[:end_revision].

1 files changed, 2 insertions, 1 deletions

diff --git a/Gemfile b/Gemfile
index d136eb5..19d92d7 100644
--- a/Gemfile
+++ b/Gemfile
@@ -45,10 +45,11 @@ gem 'acts-as-taggable-on',
     git:    'https://github.com/mbleigh/acts-as-taggable-on.git',
     branch: 'master'
 
-# ── XML / parsing ─────────────────────────────────────────────────────────────
+# ── XML / parsing / diffing ───────────────────────────────────────────────────
 
 gem 'libxml-ruby', '~> 5.0', require: 'xml'  # body link rewriting in Page model
 gem 'nokogiri',    '~> 1.18'
+gem 'diff-lcs', require: 'diff/lcs'
 
 # ── Operational ───────────────────────────────────────────────────────────────