improve error reporting in buildnumber task a little.

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@272167 13f79535-47bb-0310-9956-ffa450edef68

src/main/org/apache/tools/ant/taskdefs/BuildNumber.java

@@ -174,7 +174,7 @@ public class BuildNumber
         {
             final String message = 
                 m_file + " contains a non integer build number: " + buildNumber;
-            throw new BuildException( message );
+            throw new BuildException( message , nfe );
         }
     }
 
@@ -197,7 +197,7 @@ public class BuildNumber
         }
         catch( final IOException ioe )
         {
-            throw new BuildException( ioe.getMessage() );
+            throw new BuildException( ioe );
         }
         finally
         {