The .svn/entries file format has changed from clean XML to some weird line-based
fixed-size format, and the revision number can't be extracted.
Could switch to using the 'svnversion' helper program if present, but may not be
reliable (chroot, non-standard directory, different versions present, or just missing
because the checkout was made on another machine).
Good to figure out the new format, if it's consistent or documented. Sigh.