Fix integer overflow problem with pixel-aspect-ratio calculations in videoscale and xvimagesink (#341542)

Original commit message from CVS:
* docs/libs/gst-plugins-base-libs-docs.sgml:
* docs/libs/gst-plugins-base-libs-sections.txt:
* gst-libs/gst/video/video.c: (gst_video_calculate_display_ratio):
* gst-libs/gst/video/video.h:
* gst/videoscale/Makefile.am:
* gst/videoscale/gstvideoscale.c: (gst_video_scale_fixate_caps):
* sys/xvimage/xvimagesink.c: (gst_xvimagesink_setcaps):
* tests/check/Makefile.am:
* tests/check/libs/video.c: (GST_START_TEST), (video_suite),
(main):
Fix integer overflow problem with pixel-aspect-ratio calculations
in videoscale and xvimagesink (#341542)