Improve error message display

app/assets/stylesheets/bootstrap.css.scss

@@ -146,3 +146,9 @@ textarea {
 .controls > .radio:first-child, .controls > .checkbox:first-child {
   padding-top: 5px;
 }
+
+.error {
+  .help-inline {
+    color: #c00;
+  }
+}

app/models/user.rb

@@ -11,7 +11,7 @@ class User < ActiveRecord::Base
 
   validates_uniqueness_of \
     :nickname,
-    :message => "Sorry, but your nickname is already taken"
+    :message => "Sorry, but your nickname is already taken, choose different one"
 
   has_many :user_tokens, :dependent => :destroy
   has_many :asciicasts, :dependent => :destroy