[PATCH] Implement substitutions of placeholders in the replacement text of the fixits.

[Manuel Klimek]

My expectation would have been to add the user name to the config, and have a method to get the user name accessible from checks; if somebody then wants to insert a unique token for the username (such as <<<USERNAME>>>) and resolve that later, that's fine -  and it can be resolved by the outer layer (which needs to exist anyway in that case) running sed over the changed files.

http://reviews.llvm.org/D5408