Update fasd to use installed version instead of embedded

[tswicegood]

This removes the embedded version of fasd in favor of installed versions. I've included an error message when enabled and unable to find the fasd executable.

[tswicegood]

@nwinkler would appreciate a second set of eyes on this before I merge. I was trying to fix fasd swallowing $? when I did the upgrade. I have a fix that I might still apply, but this seems to fix it now though I'm not 100% sure how. Love it when that happens. 😎

Couple of things to check:

• Verify that echo $? outputs 0 if you run true and 1 if you run `false.
• Test the output of echo $PROMPT_COMMAND. I'm seeing __powerline_prompt_command running the powerline-multiline theme. Before this commit it included an eval tacked on there by fasd. That's no longer there, but all of fasd seems to be working.

[tswicegood]

FWIW, there was something up with my shell that caused this to succeed falsely. I'm in the process of removing this plugin entirely in favor of installing it and using a custom fasd --init to initialize it in bash.

[tswicegood]

Note, this PR includes a work around for clvv/fasd#72. Once that is merged we can simply replace the entire else block with eval "$(fasd --init posix-alias bash-hook bash-ccomp bash-ccomp-install)".

[tswicegood]

Ok, with the latest commits I'm back to understanding what's going on. Some ghost shell variables or something was causing it to initialize properly earlier. Going to go ahead and merge, but would still be curious for any feedback y'all have.

[edubxb]

Thanks @tswicegood for the fix, I stopped using fasd because this.

[nwinkler]

Good stuff - I had stopped using fasd because of this issue as well. Time to enable it again! Thanks for working on this!