Intermediate Clear Depth for Two-Pass Rendering Should Be 50K

[AnotherCommander]

The intermediate clear depth used in the two-pass rendering should ideally be set to 50km (actual value in MyOpenGLView.h: 50000). Currently it is 100m. Copying from the discussion that took place at issue #150:
From cim:

50000 - which is the sort of value I originally wanted for it - caused very weird
effects as you approach the planet surface. They might have been fixed now
 - I'll check. (EDIT: no, still there - for some reason while it works for everything
else, the planet doesn't join seamlessly when it crosses the pass boundary. If
that's fixable 50000 would be a much better value to use, but I suspect that's
post-1.82 for someone who knows OpenGL much better than I do)

From kanthoney:

I've just tried INTERMEDIATE_CLEAR_DEPTH at 50,000 and the misjoin effect
shows up on space stations as well, but not for very long at full speed. There's
a partial fix in branch two_pass_planet_slice, but there's still an atmospheric
effect I haven't tracked down.