add tests for rehash, whence, which
undo `assert_output_lines` in tests

It was a dumb idea and it wasn't even implemented perfectly.
add tests for version commands
add tests for `help` and `rbenv --version`
Merge branch 'test-coverage' for MAXIMUM COVERAGE
improve `versions` tests by cd'ing into a clean slate
restore original IFS for hooks
test that IFS in hooks is correct

closes #379
work around bug in git 1.8.2.1 in tests

Making empty commits in tests blocked by opening the default text
editor, waiting for a message which we specified to be empty.

http://thread.gmane.org/gmane.comp.version-control.git/225529
bail out early if readlink is not available

readlink comes from GNU coreutils.  On systems without it, rbenv used to
spin out of control when it didn't have readlink or greadlink available
because it would re-exec the frontend script over and over instead of the
worker script in libexec.

Fixes #389
suggest cloning rbenv via https instead of git://
ensure cleaner PATH in test environment
rbenv exec: avoid mutating PATH

Enables shelling out from a ruby process started with rbenv to a ruby
process with a different RBENV_VERSION. Fixes #121

This removes the workaround created for #15 and solves `ruby -S` support
by setting RUBYPATH. PATH is never changed.

To illustrate how RUBYPATH changes in various configurations:

    PATH=~/bin:~/.rbenv/shims:/usr/bin:/bin
    RBENV_VERSION=1.8 ruby -S rake
    #=> executes ~/.rbenv/versions/1.8/bin/rake
    #=> RUBYPATH=~/bin:~/.rbenv/versions/1.8/bin:/usr/bin:/bin

    RBENV_VERSION=2.0 ruby -S rake
    #=> executes ~/.rbenv/versions/2.0/bin/rake
    #=> RUBYPATH=~/bin:~/.rbenv/versions/2.0/bin:/usr/bin:/bin

    RBENV_VERSION=system ruby -S rake
    #=> executes /usr/bin/rake
    #=> RUBYPATH=~/bin:/rbenv_shims_were_here:/usr/bin:/bin

    RBENV_VERSION=1.8 ruby -S rake
    #=> executes ~/.rbenv/versions/1.8/bin/rake
    #=> RUBYPATH=~/bin:~/.rbenv/versions/1.8/bin:/usr/bin:/bin
Homebrew homepage location changed
Merge pull request #428 from almog/master

 Homebrew homepage moved to a new location
Clarify the search precedence for .ruby-version files.

Closes #432 [ci skip]
Install a more recent version of Ruby in README instructions
check if completion script is readable

fixes #444
fix rehash when paths have spaces in them

fixes #450
add fish shell support