Reduce CPU usage of swing debug plugin.

Fixes CLIENT-162

Change-Id: I3d0952d281e77aa78113f7f66a251c78099b6e1a
Reviewed-on: http://gerrit.dmdirc.com/1769
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>

src/com/dmdirc/addons/swingdebug/SystemStreamRedirectThread.java

                     document.insertString(document.getLength(), rar.readLine(),
                             null);
                     document.insertString(document.getLength(), "\n", null);
+                } else {
+                    try {
+                        Thread.sleep(500);
+                    } catch (InterruptedException ex) {
+                        //Ignore
+                    }
                 }
             } catch (BadLocationException ex) {
                 running = false;