title: Relation already exists during rake migration
body: <p>I have installed a blog engine to refinerycms which is working perfectly.</p>
  
  <p>Now I have generated a migration with some table fields changes (of course not refinerycms or blog tables), but I'm getting an error:</p>
  
  <blockquote>
    <p>== CreateBlogStructure: migrating ============================================<br>
    -- create_table("refinery_blog_posts", {:id=>true})<br>
    NOTICE: CREATE TABLE will create implicit sequence "refinery_blog_posts_id_seq1" for serial column "refinery_blog_posts.id"<br>
    rake aborted!<br>
    An error has occurred, this and all later migrations canceled:</p>
    
    <p>PG::Error: ERROR: relation "refinery_blog_posts" already exists<br>
    : CREATE TABLE "refinery_blog_posts" ("id" serial primary key, "title" character varying(255), "body" text, "draft" boolean, "published_at" timestamp, "created_at" timestamp NOT NULL, "updated_at" timestamp NOT NULL)</p>
    
    <p>Tasks: TOP => db:migrate<br>
    (See full trace by running task with --trace)</p>
  </blockquote>