FMSLogo Code

Fix a recent regression that prevented sprite turtles from wrapping across the top/bottom edge

Fix an inconsequential typo in a test message

Add "SETPENSIZE 1" after "SETPENSIZE 2" to prevent strange-looking results in subsequent tests

Note that the performance of sprites was improved in FMSLogo 8.3.0.

Use modff (on float) instead of modf (on double) for computing alpha values to improve performance.
Double prevision was unnecessary since the number was converted to 0-4096, which only has 12 bits of precision.

Cleanup: inline "HDC paintDeviceContext" local variable.
It was initialized far from the location where it was used and it was only used once.

Remove some redundant computation in turtlepaste when interpolating colors.
There's no need to combine the RGB color components into a single int only to separate them into the RGB components later.

Update turtlepaste to use a single wxImage for editing the portion of the screen that it updates.
This eliminates a copy (improves both memory and speed)

Improve the performance of turtlepaste by writing all pixels to the screen at once, instead of pixel-by-pixel.
This was done to reclaim some lost performance caused by setting the scroller and zoom within the PaintDeviceContext, so that FMSLogo 8.3.0 won't be perceived to be slower than FMSLogo 8.2.0.

On my Windows 10 machine, this makes the sprite benchmark take 1/3rd the time.
On my Windows XP machine, this makes no difference.

Add a missing "const" to prevent accidental modification of a buffer