The `pwd` may return relative path if the `$PWD` is badly declared
in bash/zsh (e.g. `PWD="." bash`). To avoid the infinite loop in
`find_local_version_file()`, stop finding the version file if the
target paths are same consecutively.

This reverts commit 7edceff71ca6aa1281658f6f60ca2e48a6e3f45f, reversing
changes made to 5dea3c9e63.

Closes #524

It seems that "comm" header can't be relied on cross-platform, but that
"ucomm" is more portable. I have no idea whether it's the right value to
use here, but it seems to be doing the job.

Also strip trailing whitespace because OpenBSD 5.4 `ps` output is padded
with spaces for some reason.

Fixes #489

The non-extended regex pattern didn't work on OpenBSD so this switches
grep to extended pattern mode that seems to work consistenty on all
systems.

On other systems, we expected to find system Ruby in `/usr/bin`, but in
OpenBSD 5.4 it will be found in `/usr/local/bin`.

This replaces the limited USRBIN_ALT hack with a more generic
`path_without` function that will ensure that the given executable is
not present in the resulting PATH even if it's found in multiple
system paths.

The error was "bash: no such file or directory" and it was due to bash
being located in `/usr/local/bin` on OpenBSD 5.4 instead of `/bin` like
on other systems.

Fixed by keeping `/usr/local/bin` in PATH during the test run.

Fix rbenv on OpenBSD

Fixes #519

In Travis CI environment, Bats thinks it's outputting to an interactive
terminal, so it switches to "pretty" format and ANSI escape codes which
don't look well in the final output.

Some tests assumed that the `ruby` executable will be found in system PATH.

Fixes #512, closes #514

ignore cache directory used by ruby-build

Remove Neckbeard reference in favor of Advanced

Fish user config file `~/.config/fish/config.fish` loads for every
instance of fish shell, not just interactive ones. Since it's
unnecessary and dangerous to eval `rbenv init -` output in
non-interactive shells, wrap the invocation in a conditional that checks
if the current shell is interactive.

Fixes #501

There is filterdiff(1) available to transform strip level of a patch if
optional level is required.

```
git diff HEAD^ | filterdiff --strip=1 | pyenv install -p 3.3.3
```

Imported changes from sstephenson/rbenv#453.

Could not install setuptools 2.0.1 for jython-2.7-beta1 by the
lack of `parser` module.