having Marble find the right data files

[Dirk Hohndel]

One of the challenges with the Google Maps update to Marble that I just
pushed is that it requires the user to move two directories to a
specific spot in their home directory (on Linux - I haven't checked how
this would work on Mac or Windows).

That's of course not a sustainable idea for a bundled application.

Marble supports a global variable named MarbleDataPath that allows us to
set one (of two) search path for Marble to find its data files. What
Marble doesn't support today is ':' separated multiple paths that it
would search, but we can indeed set things up that Subsurface searches
for the files and then sets up the MarbleDataPath accordingly.

I think we need to make these platform dependent functions that do
something like this:

If subsurface is run from the local directory, then MarbleDataPath="."
If subsurface is installed by make install (or as an application
package), then MarbleDataPath is set to a system specific install
directory (%executable_path%/../Resources/lib/marble or something like
that on Mac).

I think we can do this in a clean and consistent way on all three OSs.

Volunteers?

/D