Last weeks changes took away helpful information about why exec failed to run; this puts it back in.

git-svn-id: https://svn.apache.org/repos/asf/ant/core/trunk@270068 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -323,7 +323,7 @@ public class ExecTask extends Task {
             runExecute(exe);
         } catch (IOException e) {
             if (failIfExecFails) {
-                throw new BuildException("Execute failed: ",e, location);
+                throw new BuildException("Execute failed: "+e.toString(),e, location);
             } else {
                 log("Execute failed: "+e.toString(), Project.MSG_ERR);
             }