The `svn commit` command does not detect changed files unless
their mtime has changed. A quick succession of, for instance,
`svn co ...; echo x >> y; svn ci` can thus lead to the change to y
being ignored.
Edited by pmezard to write in binary mode.
In some subversion repositories, trunk is present but no branches
are used. The current code is assuming that both trunk and branches
must exist before adding trunk's head to the heads list.
It's just better to separate the branch layout stuff from the trunk one.
