Comment 3 for bug 248333

I've proposed a branch that makes the check for executability per-tree rather than OS-specific.

The next step would be to extend the per-tree test to see if the current file system actually supports the executable bit. This can be done by:

 * statting a file (probably .bzr/format), and looking at st_dev
 * using getmntent to find the right entry in /proc/mounts
 * checking if the filesystem found is known to support or not support the executable bit