- The zoomable_region widget now uses exponential rather than linear
     zoom scaling since this is much more pleasing to use.  There is now
     a new requirement on the zoom increment that it must be between 0
     and 1.
   - I added a few missing requires clauses.
   - I changed the set_zoom_scale() function so that it actually changes
     the zoom scale even if the user requests a zoom value outside the
     allowed range.  It just uses the max or min allowed value rather than
     doing nothing.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403170