svnmeta: do not add instance references to the class object This is part of a bigger plan to prevent a fd leak by making sure the sqlite connection object is garbage collected. Usually this is not a very serious issue but the testing framework will run all tests in a single process by default. The fd leak will make tests fail on systems with a low RLIMIT_NOFILE. Previously, when we are adding new properties to the SVNMeta class, we bind the current instance in the closure, which essentially prevents any SVNMeta instances from being garbage collected (and its state like revmap). This patch changed "self" from the closure one to the lambda argument to address the issue.