Subversion allows revisions to be composed of subparts coming from revisions
before the parent or from other part of the repository. There is no simple
representation for these now, keep the changes but do not track their origins.
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.
