Add anaconda3 4.1.1

Remove `bin.orig` if it already exists

The directory may exist if the `build_package_symlink_version_suffix`
ran multiple times.

Add CPython 3.6.0b1 and remove 3.6.0a4

https://www.python.org/downloads/release/python-360b1/

The literal tilde in a PATH entry (e.g. `~/.rbenv/shims`) doesn't seem
to be supported by system `which` utility, but *does* seem to be
supported by `command -v` (used in `rbenv-which`) and `type -p`.

Therefore, we must strip away `~/.rbenv/shims` from PATH when looking up
executables for system Ruby, lest we risk infinite loop. We do so by
substituting any occurence of `~` in PATH with the value of `HOME`.

Added pypy2-5.4.1 and pypy-5.4.1

Updated comment and fixed typo.

Added pypy2-5.4.1-src

Added pypy-portable-5.4.1 now

Updated pypy2-5.4 with portable pypy links

Added pypy-portable-5.4

Rename pypy 5.x definitions as `pypy2`

Added pypy-5.4-src

make all http source urls https

The plugin pyenv-default-packages uses `$(pyenv root)/default-packages`
as configuration file. Since this plugin is listed as approved, I
assume it makes sense to have the file permanently ignored by Git.

Add CPython 3.6.0a4; remove 3.6.0a1 and 3.6.0a3

https://www.python.org/downloads/release/python-360a4/

Show meaningful message on missing executable (fixes #610)

Split blacklist of conda's system executables

The performance issue must be caused by too many I/O requests to
`conda.txt` from fgrep. This inline expansion should work to reduce # of
read to the `conda.txt`.

original performance:

```
% git rev-parse HEAD
4f76be6a12
% time bash -c 'pyenv rehash'
bash -c 'pyenv rehash'  0.05s user 0.02s system 76% cpu 0.089 total
```

previous commit: ==> 4x slower than original

```
% git rev-parse HEAD
4469d51ef7
% time bash -c 'pyenv rehash'
bash -c 'pyenv rehash'  0.06s user 0.03s system 25% cpu 0.358 total
```

with this workaround: ==> almost same as original

```
% git rev-parse HEAD
3ffe91bdbc
% time bash -c 'pyenv rehash'
bash -c 'pyenv rehash'  0.05s user 0.00s system 68% cpu 0.082 total
```

rbenv 20160815