pyenv 20140614

Changes:

* pyenv: Change versioning schema (`v0.4.0-YYYYMMDD` -> `vYYYYMMDD`)
* python-build: Add new PyPy release; pypy-2.3.1, pypy-2.3.1-src
* python-build: Create symlinks for executables with version suffix
* python-build: Use SHA2 as default digest algorithm to verify downloaded archives
* python-build: Update default setuptools version (4.0 -> 4.0.1)
* python-build: Import recent changes from ruby-build v20140524