Add `rbenv versions --skip-aliases` option

The symlinks weren't correctly resolved if they were pointing to a
single path component, such as `ln -s foo bar`.

Useful in combination with `--bare` to list just the unique version
numbers without the extra directory entries that are symlinks to other
version numbers in the same directory.

BASH_SOURCE might be more reliable.

Closes #809, references #806

This is for Linux desktop platforms that have Terminal application
configured to start shells in interactive but not login mode. Creating a
`~/.bash_profile` would also cause `~/.profile` to not run, which might
be a problem on Ubuntu which ships with a default `~/.profile`.

Avoid running `rbenv rehash` multiple times during `bundle install`

This avoids running `rbenv rehash` after installing libraries that don't
have executables, or after a no-op `bundle install` that didn't install
anything.

This is an attempt to work around the fact that Rubygems post_install
hooks may happen multiple times per single `bundle install` and ideally
we want `rbenv rehash` to run only once if new gems have been installed.
However, due to Bundler parallelism using `fork` on platforms that
support it, it's impossible for the child processes to communicate with
the master process to signal it to run `rbenv rehash` in the end.

This hooks into Bundler `install` command and runs `rbenv rehash` after
all gems have finished installing, but only if the install location was
system gems location and not a custom path (such as per-project
`vendor/bundle`).

This is limited because we can't tell whether any gems have been
installed at all, let alone do those gems have executables. However it's
better than having multiple `rbenv rehash` being run in parallel and
outputting confusing error messages as a result.

When `rbenv --version` is called, this now happens:

1. It changes into the directory where `libexec/rbenv--version` resides
   and checks if it's a checkout of the rbenv repo (as opposed to
   Homebrew checkout or something else). Then it reads the git revision.

2. If that failed, change to `$RBENV_ROOT` directory and repeat step 1.

Use `command` to run rbenv rehash

Closes #529

If set by the user's environment, `git config --global` writes will go
to that destination instead of temporary $HOME. We definitely don't want
that.

Fixes #742

rbenv-init: do not use basename for $shell

Include gems dir in .gitignore

Closes #725

Display version origin with non-installed versions

This is useful as an indicator where it is coming from.

Provide uninstall instructions in the README

It's not that this is a preferred way to set a global version (one
should use `rbenv global <version>` instead), but this fixes the
function purely for correctness: all parent directories should be
scanned, even the root directory.

Fixes #745

This can be done using bash directly.

Fix test for adding shims in fish

Commit e2173df4 (for issue #369) did not handle the fish test properly.

This renames it and fixes the assertion.

Closes #699, fixes #666 [ci skip]

Fix pattern replacement to allow flags with commas.

Remove dead links to History and License from README

Cfr. #688

Remove history, license information from README

Remove warning about extraneous "ruby-" prefix in `.ruby-version`

Update README to make rbenv version consistent with previous `versions` output

The `rbenv versions` info highlights 1.9.3-p327 as the current version, and
making `rbenv version` sample output match that helps make it clearer.

[README] Updated link to bundler.io

The license information is already present in the LICENSE file.

We won't maintain it anymore. Instead, the changelogs can be obtained
from the project's Releases page: https://github.com/sstephenson/rbenv/releases

When we started to support reading `.ruby-version` files, we made a
commitment to not support fuzzy version matching. Treating "ruby-2.1.5"
as "2.1.5" is a sort of fuzzy matching, so we put in place a warning
telling you to remove the extraneous "ruby-" prefix popularly used by
other Ruby version managers to denote MRI. (Their logic is that MRI is
"ruby" and other rubies are not "ruby", apparently.)

However, people are often not able to remove the prefix in their
projects because they want to support other coworkers and tools that
sadly still require the prefix, like RubyMine.

So to restore sanity for a big portion of our users, the warning is gone.

Since communal-gems is maintainer-approved, thought it would be useful to include the directory it uses in the ignore list.

(This also helps me, since I install rbenv as submodule and without this entry, the submodule is perpetually marked dirty.)