Gtk3 master

[Robert Fewell]

Just tried to build from master after all the recent changes and it failed
on guile, currently I am running 1.8 and in the log file I see "Using
guile-1.8.x" but it then logs "The guile executable was not found, but is
required. Please set GUILE_EXECUTABLE." Looking at CMakeLists.txt, I can
build if I comment out the four lines starting at 283. Not sure if they are
required or should be moved so will leave for some one who knows what they
are doing.

On a similar note, I still do a build on my Gtk3.10 VM but have to change
line 195 as it states the version should be greater or equal to 3.14, is
this just a typo or have I got the minimum version wrong ?

Bob