COMPILER enhancement (edit 627) adds new conditional compilation statements:
++ELIFDEF <symbol>
++ELIFMAP <var>
++ELIFDEF is to ++IFDEF, and ++ELIFMAP is to ++IFMAP, as ++ELIF is to ++IF.
Note that ++ELIF, ++ELIFDEF, and ++ELIFMAP can be intermixed. For example:
++IFDEF CODE_BLUE
++MESSAGE Warning: Code Blue!
++ELIFDEF CODE_RED
++MESSAGE Warning: Code Red!
++ELIFMAP COLOR'VAR
++MESSAGE COLOR'VAR variable is mapped
++ELSE
++MESSAGE No colors defined or mapped
++ENDIF
