When a brower specified in an External Browser (Unix) object is not in the 
user's path or does not have execute permissions, the exception below is 
thrown.  In the case of External Browser (Command Line) an error message is 
given instead.  We should probably have the same error message for both browser 
types.

java.io.IOException: netscape: not found
        at java.lang.UNIXProcess.forkAndExec(Native Method)
        at java.lang.UNIXProcess.<init>(UNIXProcess.java:54)
        at java.lang.Runtime.execInternal(Native Method)
        at java.lang.Runtime.exec(Runtime.java:551)
        at java.lang.Runtime.exec(Runtime.java:418)
        at java.lang.Runtime.exec(Runtime.java:361)
        at java.lang.Runtime.exec(Runtime.java:325)
        at org.netbeans.modules.extbrowser.UnixBrowserImpl.setURL(UnixBrowserImp
l.java:159)
        at org.openide.awt.HtmlBrowser$1.run(HtmlBrowser.java:398)
        at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:154)
        at java.awt.EventQueue.dispatchEvent(EventQueue.java:331)
        at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchTh
read.java:134)
        at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThre
ad.java:101)
        at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:96)
        at java.awt.EventDispatchThread.run(EventDispatchThread.java:88)