When a mode has 2 very close refresh rates such as 59.94Hz and 60Hz,
most of the time, we'll want the 59.94Hz version.
Hide the "PC" 60Hz version and only show the 59.94Hz version in those
cases, and mark the frequency as "60Hz (ATSC)" so that those
knowledgeable know that it's really 59.94Hz, and doesn't confuse those
who expect rates to be multiple of 30Hz or 25Hz.
See also https://en.wikipedia.org/wiki/NTSC#Lines_and_refresh_rate
Note that we also do this for half and double that rate, eg. close to
~30Hz and ~120Hz.
https://bugzilla.gnome.org/show_bug.cgi?id=655041
529b29cae9