fixes #374
The problem was in the map year2rev that maps from a year to the last
revision of that year. We got that information from an SVNlog(ROOT)
object. When ROOT was yat/yat the problem (we've seen before)
occured. The problem is that if we follow the log of yat/yat we
realize it was created in 2005, so the map wouldn't cover for year
2004 and 2003. And there are many files, for example
yat/yat/Makefile.am, that were created in 2003 and 2004.
I could see two obvious solutions to the problem. Either call get the
log from repos_root_url or call NODE::log. The latter gives the union
of the logs of nodes in the directory (and below), which should be
sufficient. That, however, also implies that a log call is needed for
every file, which makes this slow in particular since ROOT often is
quite high the files structure. I therefore went with a log call to
repos_root_url, which is fast since it only involves one call to svn
server.
