This allows people to disable the building of anything GUI related.
In my case, it is used for servers.
I encourage anyone that think they can do a better patch to improve it,
as i dislike having to add all those AM_CONDITIONAL().
Maybe the macros should be improved.
Nightly build failed with (make doc):
cd: ../../../src/lib/eo/.libs: No such file or directory
Looks like there's one too many ../
I guess the build dir is not the source dir on the build bots.
The filter code is a copy and paste from the doc.
Maybe the code should be in an include file, so we're sure the
preview and the documentation code are the same?