I don't think that we should enforce a coding style, but we should definitely enforce an indent style:
- No tabs.
- No trailing white spaces.
- 4 spaces to indent the code.
In addition to Jon's suggestion for fixing up old files, we should also allow white space changes to a limited extend in any patch. For example, if I am touching a method in a file, I should be able to fix white spaces in that area of code that I'm touching regardless how long that file has not been modified. Fixing an entire file could be disruptive, but fixing parts of a file should be acceptable, no?