Windows only.  During a standard (non silent) install, when the Nullsoft
installer encounters an in-use file that it's trying to write, it displays
a dialog that says "Error opening file for writing: <filename>  Hit abort to
abort installation, retry to retry writing the file, or ignore to skip this
file."  This message can be confusing to users and is not specific enough.

We should use a more specific message like
"Error opening file for writing: <filename>.  This may be due to a Java Web
Start application that is currently running.  If this is the case, it is highly
recommended that you close all Java Web Start applications and select retry.

Do you wish to abort installation, retry writing the file, or ignore the error
and continue?"

We should also present a message at the beginning of the install that recommends
closing all currently running JavaWS apps.