[pkg-fgfs-crew] Bug#793517: fltk1.3-dev cmake interface now requires libcairo2-dev and fluid?

[Rebecca N. Palmer]

Control: tags -1 patch

Since libfltk1.3-dev 1.3.3-1 switched to using upstream's cmake files 
(https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=792386#10), using it 
from cmake now appears to require libcairo2-dev and fluid, which are not 
hard Depends of the package (presumably because they aren't required 
when using it from autotools/pkg-config).

This causes fgrun 
(https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=793517) and lmms 
(https://reproducible.debian.net/rb-pkg/unstable/amd64/lmms.html) to 
FTBFS; it could also affect gmsh, zynaddsubfx and mathgl.  (yoshimi 
already had these dependencies, and freecad appears to not actually use 
FLTK.)

Adding libcairo2-dev (and fluid, where not already present) as 
build-dependencies should fix this (though I currently can't run a full 
test due to the gcc5 transition).