[Utopic SRU] Fix unconditionally exchanging short filenames

[Stefan Bader]

BugLink: http://bugs.launchpad.net/bugs/1396907
Debian: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=763831

A change in v3.15 broke the behaviour of /proc/$$/exe on rename.
Debian fixed this by pulling in those two patches. Ben, in hindsight
I could have directly pulled them from your kernel but at least I 
believe we ended up with the exact same result. But a quick sanity
check won't hurt.

Right now the same problem exists in Vivid but when we switch over
to v3.17+ this will go away anyway. So I won't bother that much there.
The only other kernel affected would be v3.15 which I believe is not
maintained by anybody. So I decicded to not submit this to @stable.

-Stefan