lptypes.h: Handle Lua 5.3 correctly
Makefile.am: Use CXX_CHECK_FLAGS in AM_CFLAGS too
Make SurfaceLight::intensity field private
Clean up Hist2dDist and DirHistDist interfaces a bit

Rename the "calc" method to "set_histogram".

Don't require the size to be pre-declared on construction, instead
just copy the size of the input histogram in set_histogram.  This is
slightly less efficient, but not in anyplace important.

Make Hist2dDist methods out-of-line, as they're fairly big and slow.
Make data fields in Hist2dDist private

There's no real reason for users to have access to them.
Add Hist2dDist::empty method
Use the term "tex_coords_uv" for clarity
Simplify Ellipse texture calculations

... there's no need to calculate texture UV coordinates, as they're
already available as a result of the intersection calculations.
Add default (uninitialized) constructor for TexCoords