Bring bashrc more inline with the regular file

- Remove a whole bunch of aliases and definitions and so forth that I'm
  not used to having or which I just don't use (with the caveat that
  they may get added back if it turns out I use them more once I'm using
  the CentosVM more in line with other folk).
- Don't run bashrc if it's not an interactive session.
- Set the PS1 to my normal style.
- Trust the terminal's assertions about itself.
- Remove unused colourful prompt code.
- Add Bash behaviour I expect to exist (bash_completion, globstar, etc).
- Add a big stack of functions of varying levels of utility to reduce
  the differences between this bashrc and my regular one.