Improve prelude-open-with

Now it uses `xdg-open` where it makes sense. It also accepts a prefix
argument that forces manual selection of a command to run.
Don't try to save files when you don't have the permissions to do so
Quote buffer-file-name in prelude-open
Simplify prelude-rename-file-and-buffer
Add autoloads for PKGBUILD and .zsh file
Add kk keychord for just-one-space
Merge pull request #320 from toctan/master

Add autoloads of major modes for PKGBUILD and .zshrc file
Do not show the tip if cursor is in the minibuffer
Bind `KK` to `delete-horizontal-space`
Merge branch 'master' of github.com:bbatsov/prelude

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Merge branch 'master' of https://github.com/bbatsov/prelude
Add session* to .gitignore
Merge pull request #321 from toctan/master

Do not show the tip if the cursor is in the minibuffer window
Describe disabling key-chords in the README

It's good to have defaults, but nice to document a way of changing them
as well.
Merge pull request #324 from Abizern/key_chord_documentation

Describe disabling key-chords in the README
Remove problematic kk keychords
Override default move-beginning-of-line behavior
Add missing whitespace
Enable manually elisp-slime-nav (fixes #325)
Fix lisp code blocks in README.