Bug #15651: Restore deleted line in comment

The deletion occured in c48bf013

src/chrome/content/torbutton.js

+// Bug 1506 P0-P5: This is the main Torbutton overlay file. Much needs to be
 // preserved here, but in an ideal world, most of this code should perhaps be
 // moved into an XPCOM service, and much can also be tossed. See also
 // individual 1506 comments for details.