FMSLogo Code

Move numeric_arg from graphics.cpp to logmath.cpp and make it static.
After recent refactoring, logomath.cpp is the only place remaining that calls it.

Change lscrollx() and lscrolly() to use flonum_arg().
flownum_arg() is preferable to numeric_arg() because it doesn't have the side effect of changing the argument list.
This is part of a larger effort to make the code base simpler by removing side effects.

Add tests that bad inputs to SCROLLX/SCROLLY are recoverable with :erract.

Add EVALTEST.SILENTLOADFROMTREEIFY.SYNTAXERROR
This is similar to EVALTEST.SILENTLOADFROMTREEIFY.THROWSERROR, expect it
exercies a different code path and causes the stopping_flag to be set to STOPPING when treeifying.

Add EVALTEST.RETREEIFYFROMRETREEIFY
This test is constructed such that retreeify_running_proc_body is called from the context of retreeify_running_proc_body via silent_load.

Note that Bug #249 is fixed in FMSLogo 8.6.0.
This was incidentally fixed when Bug #620 was fixed.

Add EVALTEST.SILENTLOADFROMTREEIFY.THROWSERROR
This tests the "silent" aspect of the silent loading from treeify
because the file that gets loaded throws an error.

This was not as silent as I had thought.
The error doesn't stop the treeification, but it prompts
the user to fix the file in the editor.
That may be a bug.

Extend the build system to compile a 64-bit version of FMSLogo on Windows.
This is clumsy (for example, there's a separate obj64 directory instead of reusing obj) but it works.
The only thing that I know didn't port is DLLCALL, which currently throws an error.
Getting DLLCALL to work will require some assembly code to follow the X64 calling convention.

Update the expected test results to include new tests that were added and new bugs that were fixed.

Fix typos in a comment