DefaultArtifactInstaller should only overwrite files if timestamp has changed

install:install (from maven-install-plugin) by default uses DefaultArtifactInstaller to install artifacts. DefaultArtifactInstaller in turn uses FileUtils.copyFile(), thereby overwriting destination files even if they are unchanged. It would be helpful if DefaultArtifactInstaller used FileUtils.copyFileIfModified() instead, at least as an option, to speed up the build process.