Limit length of the commit id in produced archive

 + 10 characters are pretty enough to identify a commit uniquely, according to
 most sources:

http://stackoverflow.com/questions/18134627/how-much-of-a-git-sha-is-generally-considered-necessary-to-uniquely-identify-a
(especially http://git-scm.com/book/en/v2/Git-Tools-Revision-Selection#a-short-note-about-sha-1-ArUocySYSw)
More background: https://git.kernel.org/cgit/git/git.git/commit/?id=dce96489162b05ae3463741f7f0365ff56f0de36

pkg.sh

@@ -9,7 +9,7 @@ if ! [ -e dist ]; then
 fi
 
 # If no tag, use commit SHA1
-id=`git describe --abbrev=40 --candidates=50 HEAD`
+id=`git describe --abbrev=10 --candidates=50 HEAD`
 name=oclaunch_${id}_src # _src emphasis the difference with binary tarballs
 
 echo "Writing in" $name".*"