[plt-scheme] change in color-prefs in the framework

EXECUTIVE SUMMARY: do not use the same names for v370 color
preferences as you used for v360 color preferences, or users who go
from v370 back to v360 will not be able to start up v360. (I have
dealt with this in all the code the plt SVN archive.)

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There was an annoying bug in the framework that means that we have to
rename all of the color preferences for v370.

The bug: the unmarshaller signals a runtime error when the preference
saved on disk doesn't match the format of a marshalled preference (the
marshallers should just give back the default or do something sensible
in that case). It matters because the coloring can now includes the
smoothing setting, which wasn't being saved before, so the format on
the disk has changed.

So, this means that, if we didn't rename some preference, that a user
who starts up v370, changes a color pref, would then be unable to
start v360 (it would fail with a runtime error when trying to
unmarshall the v370 preference).

Anyways, I've renamed all uses in the SVN tree. They were in these collections:

  framework
  drscheme
  profj

I've also renamed the functions that deal with these preferences, so
your code won't compile, in the case that your code would need to be
changed. Please don't just rename the functions to match their new
names! Change the preference, too.

Thanks,
Robby