Optimize pyenv-which: implement remove_from_path in Bash

This greatly improves the performance of `pyenv virtualenvwrapper_lazy`,
which happens to call pyenv-which a lot.

For profiling I've initially used:

    % zmodload zsh/zprof
    % eval "$(pyenv init -)"
    % pyenv virtualenvwrapper_lazy

    Before:
    % zprof|grep -E '(pyenv|virtualenv)'
     1)    1         754,07   754,07   58,95%    751,50   751,50   58,75%  pyenv
    21)    1           2,57     2,57    0,20%      2,57     2,57    0,20%  virtualenvwrapper_setup_lazy_loader
     1)    1         754,07   754,07   58,95%    751,50   751,50   58,75%  pyenv
           1/1         2,57     2,57    0,20%      2,57     2,57             virtualenvwrapper_setup_lazy_loader [21]
           1/1         2,57     2,57    0,20%      2,57     2,57             pyenv [1]
    21)    1           2,57     2,57    0,20%      2,57     2,57    0,20%  virtualenvwrapper_setup_lazy_loader

    After:
    % zprof|grep -E '(pyenv|virtualenv)'
     1)    1         383,30   383,30   27,97%    380,88   380,88   27,79%  pyenv
    31)    1           2,42     2,42    0,18%      2,42     2,42    0,18%  virtualenvwrapper_setup_lazy_loader
     1)    1         383,30   383,30   27,97%    380,88   380,88   27,79%  pyenv
           1/1         2,42     2,42    0,18%      2,42     2,42             virtualenvwrapper_setup_lazy_loader [31]
           1/1         2,42     2,42    0,18%      2,42     2,42             pyenv [1]
    31)    1           2,42     2,42    0,18%      2,42     2,42    0,18%  virtualenvwrapper_setup_lazy_loader

Fixes https://github.com/yyuu/pyenv-virtualenvwrapper/issues/13
Add miniconda/miniconda3 3.4.2
v20140516
Update pip (1.5.5 -> 1.5.6)
Merge pull request #169 from makotosasaki/2

Update pip (1.5.5 -> 1.5.6)
Add CPython 3.4.1
Merge pull request #171 from makotosasaki/2

Add CPython 3.4.1
v20140520
Check envvars of `CPPFLAGS` and `LDFLAGS` during tests
Don't clober the environment `CPPFLAGS` and `LDFLAGS` (refs #168)

Because the variables specified via command-line arguments for the
`./configure` will be favored than one in environment variables,
setting those variables in `PACKAGE_CONFIGURE_OPTS_ARRAY` will hide
existing environment variables.

To avoid the problem, stop using `package_option()` to setup those
variables.
Merge branch 'dont_clober_ldflags_cppflags' (fixes #168)
Can't install Jython 2.7 Beta 2
Support for xz-compressed Python tarballs (fixes #177)
Add CPython 2.7.7rc1 (refs #178)
Add Anaconda and Anaconda3 definitions for v2.0.0
Merge pull request #179 from thomasjo/anaconda-2.0

Add Anaconda and Anaconda3 definitions for v2.0.0
Add CPython 2.7.7 (refs #180)
Update setuptools (3.6 -> 4.0) (refs #181)
v20140602
Update setuptools (4.0 -> 4.0.1) (refs #183)