Restore and fix -flipPixels option
Please refer #1057 (closed) for details. These changes have been appiled NetBSD's local tree: https://github.com/NetBSD/xsrc/commit/9b06bd197b8d655bbc737e19322aba55da68c484 https://github.com/NetBSD/xsrc/commit/b2450a3ad0f57f762808ccfb1c3db9e5450b8376