Simplify "is assignment" check and move it to JetPsiUtil

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetPsiUtil.java

@@ -37,6 +37,7 @@ import org.jetbrains.jet.lang.types.expressions.OperatorConventions;
 import org.jetbrains.jet.lang.types.lang.KotlinBuiltIns;
 import org.jetbrains.jet.lexer.JetToken;
 import org.jetbrains.jet.lexer.JetTokens;
+import org.jetbrains.jet.util.QualifiedNamesUtil;
 
 import java.util.Collection;
 import java.util.HashSet;
@@ -621,4 +622,9 @@ public class JetPsiUtil {
         int parentPrecedence = getPrecedenceOfOperation(parentExpression, parentOperation);
         return innerPrecedence < parentPrecedence;
     }
+
+    public static boolean isAssignment(@NotNull JetElement element) {
+        return element instanceof JetBinaryExpression &&
+               JetTokens.ALL_ASSIGNMENTS.contains(((JetBinaryExpression) element).getOperationToken());
+    }
 }

compiler/frontend/src/org/jetbrains/jet/lexer/JetTokens.java

@@ -195,4 +195,5 @@ public interface JetTokens {
             IDENTIFIER, LABEL_IDENTIFIER, ATAT, AT);
 
     TokenSet AUGMENTED_ASSIGNMENTS = TokenSet.create(PLUSEQ, MINUSEQ, MULTEQ, PERCEQ, DIVEQ);
+    TokenSet ALL_ASSIGNMENTS = TokenSet.create(EQ, PLUSEQ, MINUSEQ, MULTEQ, PERCEQ, DIVEQ);
 }