In the new unified font handling, my strategy so far for combining

In the new unified font handling, my strategy so far for combining
client- and server-side fonts into a single namespace was mainly to
hope there would naturally be no collisions, and to provide
disambiguating "client:" and "server:" prefixes for manual use in
emergencies.

Jacob points out, however, that his system not only has a namespace
clash but worse still the clash is at the name "fixed", which is our
default font! So, modify my namespace policy to use the
disambiguating prefixes everywhere by default, and use _unprefixed_
names only if the user types one in by hand.

In particular, I've changed the keys used to store font names in
Unix saved session files. Font names read from the new keys will be
passed straight to the new unifont framework; font names read from
the old keys will have "server:" prepended. So any existing
configuration file for GTK1 PuTTY should now work reliably in GTK2
PuTTY and select the same font, even if that font is one on which
your system (rather, your client+server combination) has a font
namespace clash.

[originally from svn r7973]