Merge pull request #119 from github/ensureprefix

Ensure the installation prefix exists before installing into it

script/install.sh.example

@@ -6,6 +6,8 @@ elif [ "$BOXEN_HOME" != "" ] ; then
   prefix=$BOXEN_HOME
 fi
 
+mkdir -p $prefix/bin
+
 rm -rf $prefix/bin/git-media*
 for g in git*; do
   cp $g "$prefix/bin/$g"