When core.ignoreCase, check for changed files case-insensitively

Fixed #586. Include a note about the inconsistent behavior when
ignoreCase is not set to match the case-sensitivity of the file-system
itself.

Author: nevinera

Diff for: lib/git/status.rb

@@ -34,7 +34,11 @@ def changed
     #     changed?('lib/git.rb')
     # @return [Boolean]
     def changed?(file)
-      changed.member?(file)
+      if ignore_case?
+        changed.keys.map(&:downcase).include?(file.downcase)
+      else
+        changed.member?(file)
+      end
     end
 
     # Returns an Enumerable containing files that have been added.
@@ -264,5 +268,15 @@ def fetch_added
         end
       end
     end
+
+    # It's worth noting that (like git itself) this gem will not behave well if
+    # ignoreCase is set inconsistently with the file-system itself. For details:
+    # https://git-scm.com/docs/git-config#Documentation/git-config.txt-coreignoreCase
+    def ignore_case?
+      return @_ignore_case if defined?(@_ignore_case)
+      @_ignore_case = @base.config('core.ignoreCase') == 'true'
+    rescue Git::FailedError
+      @_ignore_case = false
+    end
   end
 end

Diff for: tests/units/test_status.rb

@@ -106,6 +106,7 @@ def test_added_boolean
   def test_changed_boolean
     in_temp_dir do |path|
       git = Git.clone(@wdir, 'test_dot_files_status')
+      git.config('core.ignorecase', 'false')
 
       create_file('test_dot_files_status/test_file_1', 'content tets_file_1')
       create_file('test_dot_files_status/test_file_2', 'content tets_file_2')
@@ -117,6 +118,13 @@ def test_changed_boolean
 
       assert(git.status.changed?('test_file_1'))
       assert(!git.status.changed?('test_file_2'))
+
+      update_file('test_dot_files_status/scott/text.txt', 'definitely different')
+      assert(git.status.changed?('scott/text.txt'))
+      assert(!git.status.changed?('scott/TEXT.txt'))
+
+      git.config('core.ignorecase', 'true')
+      assert(git.status.changed?('scott/TEXT.txt'))
     end
   end