Fix schema and migration for postgres

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

db/migrate/20121115094430_increate_trace_colunm_limit.rb

 class IncreateTraceColunmLimit < ActiveRecord::Migration
   def up
-    change_column :builds, :trace, :text, :limit => 4294967295
+    change_column :builds, :trace, :text, :limit => 1073741823
   end
   def down

db/schema.rb

@@ -18,7 +18,7 @@ ActiveRecord::Schema.define(:version => 20131023103430) do
     t.string   "ref"
     t.string   "status"
     t.datetime "finished_at"
-    t.text     "trace",       :limit => 2147483647
+    t.text     "trace",       :limit => 1073741823
     t.datetime "created_at",                        :null => false
     t.datetime "updated_at",                        :null => false
     t.string   "sha"