Remove empty svn:mergeinfo properties so it won't get in the way during

future merges.

The server and the repository are Subversion 1.4.x: they are unable to
understand this property.

Subversion 1.5.x clients usually won't commit it on purpose when the
server and/or the repository are 1.4.x. But they will copy it when doing
WC-to-WC copy because they do not communicate with the server at this
time.

SVN Revision: 1831