Add a line to the state file for each guard to let us know which version added the guard.  If the line is absent, assume the guard was added by whatever version of Tor last wrote the state file.  Remove guards if the version that added them was using a bad guard selection algorithm.  (Previously, we removed guards if the version that wrote the file was using a bad guard selection algorithm, even if the guards themselves were chosen by a good version.) 


svn:r11298