Use CtrlP caching if >2000 files in directory

Source:
<https://github.com/henrik/dotfiles/commit/8a8dd7b84437bbce0e37198067ee425aa8b1de97>
Alias df to `df -h`

I always want human readable file sizes.
Improve matching of whitespace around hashrocket
Silence search errors

The main purpose of this is to silence `E486: Pattern not found`.