AVATAR design: new syntax checker, and support of else guards

executablecode/Makefile.src

src/avatartranslator/AvatarBlock.java

src/avatartranslator/AvatarSpecification.java

src/avatartranslator/AvatarSyntaxChecker.java

src/avatartranslator/AvatarTransition.java

src/avatartranslator/toexecutable/AVATAR2CPOSIX.java

src/myutil/BoolExpressionEvaluator.java

src/ui/AvatarDesignPanelTranslator.java

src/ui/GTMLModeling.java