Add fix for Bug 3326 - WidgetPreInstaller.mmp does not have correct USERINCLUDE for widgetinstaller.h
The headers in this directory are for compiling on Mac OS X 10.4.
The Mac OS X 10.4 release includes the ICU binary, but not ICU headers.
For other platforms, installed ICU headers should be used rather than these.
They are specific to Mac OS X 10.4.