Now go into your sage branch:

cd sage/devel/sage

and set up for mercurial queues: 

../../sage -hg qinit

This only needs to be done *once* per installed copy of sage.

Go to trac, find your patch of interest, left click on the download box, and "copy link."   Now you will import it into your sage library:

../../sage -hg qimport <past link>

push it into the stack

../../sage -hg qpush

and rebuild your sage

../../sage -b

Now you have installed the patch into sage!