another installer build fix

installer/java/src/net/i2p/installer/Exec.java

 package net.i2p.installer;
 
 import java.io.File;
+import java.io.IOException;
 
 /**
  * <p>This class can be used by the installer to execute shell commands.</p>
@@ -20,7 +21,8 @@ public class Exec {
             // http://cephas.net/blog/2004/03/23/external_applications_javas_runtimeexec.html
             try { proc.exitValue(); } catch (Throwable t) { }
             Runtime.getRuntime().halt(0);
-
+        } catch (IOException e) {
+            e.printStackTrace();
         } catch (RuntimeException e) {
             e.printStackTrace();
         }