"sage -i" should only run sage-location if it exists

Imported from <a href="http://trac.sagemath.org/sage_trac/ticket/14303">trac #14303</a>.

root repo

Reported by: jhpalmieri

Component: build

CC: jdemeyer

Report Upstream: N/A

Authors: John Palmieri

Dependencies: 

Work issues: 

Reviewers: Jeroen Demeyer

Merged in: sage-5.9.beta1

Attachments: <ol><li><a href="http://trac.sagemath.org/sage_trac/attachment/ticket/14303/trac_14303-location.patch">trac_14303-location.patch: root repo</a> by jhpalmieri at 20130319T15:23:30</li></ol>