Using (str tag) instead of (name tag) when reading tagged literals

In order to support proper edn tagged elements (which must contain a prefix
component) we must use the full symbol (not just it's name) when looking up
and assoc'ing the the tag in *tag-table*
Support for default tag parser

If tag is not found in *tag-table* looks for *default-data-reader-fn* which is
a function of 2 arguments: tag and value
Helper functions register-default-tag-parser! and deregister-default-tag-parser!
(akin to register-tag-parser! and deregister-tag-parser!)
Tests for namespaced tags and default-tag-parser
CLJS-435: Stack overflow error when adding large numerical keys to maps

IHash implementation for numbers now apply modulo MAX INT on the floor
of the number.
CLJS-179: (ns 'foo) throws REPL into infinite loop

Used Craig Brozefsky's diff, assert that the namespace name is a symbol.
Simplify lower-case and upper-case.
CLJS-424: Use colon in keyword representation
CLJS-447: Throw exception if multiple namespaces are required with the same alias

Track aliases in parse 'ns. Throw on duplicate name.
CLJS-447: Allow each ns alias to be used up to twice

Each alias can now be used up to twice, once for a fn namespace and
once for a macro namespace. This allows the following (which had
worked before 7be3051):

(ns foo.user
  (:require [foo.core :as f])
  (:require-macros [foo.core :as f]))
Merge branch 'master' into crossing
Added Jira link
Merge branch 'master' of git://github.com/clojure/clojurescript into crossing
Warn on invalid js forms. refs #455
Merge branch 'master' of git://github.com/clojure/clojurescript into crossing
add a tutorial link
Merge branch 'master' of git://github.com/clojure/clojurescript into crossing
CLJS-358: eliminate state shared among Rhino REPL envs; can now restart REPL / use >1 Rhino REPL per Clojure runtime
CLJS-460: make MultiFn use custom hierarchy when specified

Includes a basic test.
`get-in` behaves incorrectly on values

Values which don't satisfy `ILookup` are handled incorrectly.
CLJS-459: fix reduce-kv node visit order for sorted maps

Includes a basic test.