English string changes in r2457

[cor...@corsix.org]

This is an automated message to notify translators that changes have been made
to the English translation file, which usually indicates that equivalent
changes should be made to the other translation files. The changes in r2457 are:
Strings which have been added:
tooltip.update_window.download
tooltip.update_window.ignore
update_window.caption
update_window.current_version
update_window.download
update_window.ignore
update_window.new_version