added support for Integer > Float conversion.

Moved some tests from EvaluationTests into OperatorTests.
Fleshed out OperatorTests to verify type promotions for mixed type operands.

org.springframework.expression/src/main/java/org/springframework/expression/spel/ast/OperatorPlus.java

@@ -26,7 +26,6 @@ public class OperatorPlus extends Operator {
 		super(payload);
 	}
 
-	// TODO OperatorPlus is lacking a bit on implementation...
 	@Override
 	public Object getValue(ExpressionState state) throws EvaluationException {
 		SpelNode leftOp = getLeftOperand();

org.springframework.expression/src/main/java/org/springframework/expression/spel/standard/StandardTypeConverter.java

@@ -220,11 +220,15 @@ public class StandardTypeConverter implements TypeConverter {
 
 	private static class ToFloatConverter implements StandardIndividualTypeConverter {
 		public Object convert(Object value) throws SpelException {
-			return ((Double) value).floatValue();
+			if (value instanceof Integer) {
+				return ((Integer)value).floatValue();
+			} else {
+				return ((Double) value).floatValue();
+			}
 		}
 
 		public Class<?>[] getFrom() {
-			return new Class<?>[] { Double.class };
+			return new Class<?>[] { Double.class, Integer.class };
 		}
 
 		public Class<?> getTo() {