1. Fix a misspelled variable to avoid shell namespace pollution
2. Remove a bogus completion (the 'brew xo' one)
3. Add missing tab completion code for
- Several arguments/commands (options, --cellar etc.)
- Aliases (e.g. home and homepage)
- 'brew edit' complete to all formulae, not just installed ones
Signed-off-by: Adam Vandenberg <flangy@gmail.com>