pyenv v0.4.0-20131217

Changes in this release are below.

Changes:

* python-build: Add new CPython releases; 3.3.3
* python-build: Add new CPython releases candidates; 3.4.0b1
* python-build: Add new PyPy releases; pypy-2.2.1, pypy-2.2.1-src
* python-build: Update default setuptools version (1.3.2 -> 2.0)
* python-build: Imported recent changes from ruby-build v20131211
* python-build: Fix broken build of CPython 3.3+ on Darwin
* python-build: Not build GNU Readline uselessly on Darwin
* pyenv: Fix pyenv-prefix to trim "/bin" in `pyenv prefix system`