Eclipse Plugin should ignore files generated with QMAKE_EXTRA_COMPILERS

The Qt Eclipse integration ignores certain files that are generated by Qt's build system such as those beginning with "moc_", "ui_", etc. This prevents Eclipse from trying to add them to the project file. However there is a variable that is supported in 'qmake' called QMAKE_EXTRA_COMPILERS which can also generate files and the integration should also ignore these generated files.