xrandr: look for providers by name or xid

xrandr: look for providers by name or xid

Use the name_t infrastructure to allow specifying providers by name, index, or
XID.  This means that numbers without a "0x" prefix will now be interpreted as a
indices rather than XIDs.  To match that, print provider XIDs in hexadecimal.

Print an error if a provider-related option is specified and RandR 1.4 isn't
supported.

Make get_screen robust against being called multiple times.

Signed-off-by: Aaron Plattner <aplattner@nvidia.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>