FMSLogo Code

Add a comment to LL speculating on its history and purpose.

Add some regression tests that BITLOAD loads small bitmaps at the turtle's position and large ones at 0,0 window coordinates.

Add some bitmaps that can be used to test that BITLOAD puts large images in the upper left corner and small images at the turtle.

Fix Bug #579; BITMAPTURTLE turtles are now drawn in correct position when zoomed.
This was fixed by using a backbuffer for both sprites and legacy bitmapped turtles (before, legacy bitmapped turtles were rendered without a backbuffer, which required special handling).
This will reduce the performance of programs that only used legacy bitmapped turtles.

Note that bug #24 is fixed.
Also note that loading some corrupt bitmaps may have different behavior.

Disable handling alpha channels in 32bpp bitmaps.
As far as I know, .bmp files do not have an alpha channel. What's more, this code prevented truncated 32-bpp bitmaps from being rendered in the same way that truncated 24bpp bitmaps are rendered.

Enable the "topdown" tests for 16BPP bitmaps.
These had been failing because due to a test bug (they were using the wrong file name). The images load correctly.

Fix a regression in CHECKSCREEN that used the wrong file extension for the per-computer reference data.

Update CHECKSRCREEN to be able to read expected values from "referencedata".
This makes setting up a new test machine easier, as the setup won't require manually approving as many expected data files.
This only became worthwhile after integrating bmptestsuite into the tests.

Cleanup: Remove three redundant tests (copy&paste error)