bug#9663: 23.2; feature wish: put priority on vcursor overlay

[Hendrik Tews]

Stefan Monnier writes:
   
   same priority. Which makes me wonder: why other overlay have
   you bumped into which has either higher priority than nil, or
   nil priority but is not larger than vcursor.
   
As I wrote in the feature wish: the locked region in Proof
General (proof-locked-span). It has priority 100, see the call to
span-raise inside proof-init-segmentation in
generic/proof-script.el.

Bye,

Hendrik