Treat <> as != rather than error
Fixes sprite_add lower-left transparency

For non-color pixels this goes unnoticed, but without this change,
colored pixels of the sprite are not removed when matching the
lower-left pixel.
Implements lower-left transparency for backgrounds

When supplying the transparency option for background_add, this change
forces same-colored pixels to be rendered transparent the same way
sprite_add does it.
Handles ^^ and XOR as logical xor operations

I may change how this works later, as this version will generate
compiler warnings regarding parenthesis.
Fixes special case for chained logical operators

When writing something like "1 and 2 and 3" or "not not not 0", commas
are erroneously inserted.  This commit corrects these cases.
Initial improvement of XOR system

Changes how XOR operates to better follow precedence rules.  More
commits may follow to handle XOR operations outside of the
objectfunctionality.h file.
Merge pull request #806 from Heathtech/master

Lower-left transparency fixes