This is done by the !SubversionPropertyRenderer, which implements the IPropertyRenderer interface introduced in r4653:
- it handles the `svn:externals` property by adding links to corresponding path inside the repository or the configured source browser (#2340)
- it handles the `svn:need-lock` property, by showing a locked icon when the property is set (#1601)
(partial merge of the source:sandbox/property-renderers-tmp branch)