In release 1.6.5 mod_dav_svn was changed (in r36720) to supply
'application/octet-stream' instead of 'text/plain' as the default MIME type for
files without an 'svn:mime-type' property. This causes an unwanted behaviour
change, preventing some Web browsers from displaying files from the repository.
See this email thread:
<http://subversion.tigris.org/ds/viewMessage.do?dsForumId=462&dsMessageId=2386773>.
The default was changed back to 'text/plain' in r39074 and back-ported to 1.6.x
in r39112, so this fix is expected to be available in release 1.6.6.