Hello, all!

I noticed that org-refile-get-targets seems to recalculate the first
part of the outline path for each heading, which makes it slow on large
files when org-refile-use-outline-path is set to 'title. The following
patch let-binds that part to a variable that can be put outside the loop
for the headings, making it faster in the case where refile targets
include a few files with lots of headings. Does it make sense? I was
wondering if I was missing some important reason for it to be inside
that loop.

It feels like a pretty small change (just adding a let), but I 
have copyright assignment papers on file at the FSF just in case.