Transactional timeout documented as seconds in annotation javadoc

Issue: SPR-17226

(cherry picked from commit 8c6f350)

Author: jhoeller

Diff for: spring-tx/src/main/java/org/springframework/transaction/annotation/Transactional.java

@@ -98,7 +98,7 @@
 	Isolation isolation() default Isolation.DEFAULT;
 
 	/**
-	 * The timeout for this transaction.
+	 * The timeout for this transaction (in seconds).
 	 * <p>Defaults to the default timeout of the underlying transaction system.
 	 * <p>Exclusively designed for use with {@link Propagation#REQUIRED} or
 	 * {@link Propagation#REQUIRES_NEW} since it only applies to newly started