Allow the svn:executable property to affect the git filemode
This allows a file to be marked executable in Git using the full
property-setting machinery, for example via `AutoPropsPropertySetter`.
We only need to check for the presence of the `svn:executable` flag
because Git already uses the `ExecutablePropertySetter`, which sets
the `svn:executable` property based on whether the CVS file had its
executable bit set.
Patch by: Mark Rotteveel <mark@lawinegevaar.nl>
git-svn-id: http://cvs2svn.tigris.org/svn/cvs2svn/trunk@5470 be7e6eca-30d4-0310-a8e5-ac0d63af7087