Fix that adding the same name multiple times wasn't idempotent

README.markdown

@@ -31,10 +31,6 @@ out their names, the current pair, and some other information.
 ## Known issues
 
 * I just shoved everything into a gem. Refactor into separate files.
-* Don't add duplicate authors to the git-config (doesn't affect the proper
-  functioning of git-pair, but makes `git pair --add` not idempotent and
-  clutters up your config file if you keep adding the same person). There's a
-  failing test for this now.
 * Test coverage is low -- I'm working on a cucumber suite.
 
 ## Feature hit list

lib/git-pair.rb

@@ -9,16 +9,25 @@ class MissingConfigurationError < RuntimeError; end
 
 
   module Commands
-    def add(name)
+    def add(new_name)
       @config_changed = true
-      `git config --add git-pair.authors "#{name}"`
+      names = Helpers.author_names.push(new_name).sort.uniq
+      remove_all
+      names.each do |name|
+        `git config --add git-pair.authors "#{name}"`
+      end
     end
 
     def remove(name)
       @config_changed = true
       `git config --unset-all git-pair.authors "^#{name}$"`
     end
 
+    def remove_all
+      @config_changed = true
+      `git config --unset-all git-pair.authors`
+    end
+
     def set_email_template(email)
       @config_changed = true
       `git config git-pair.email "#{email}"`