Enable ::makeRelativePath() again after the function has been updated

Before, the following situation would lead to a wrong serialization:

getFilename(): "path/to/file.iv"
basePath: "path"

would result in: "path/file.iv" (since fn.filename() was used instead of the complete file)

git-svn-id: http://svn.code.sf.net/p/simox/code/trunk@559 042f3d55-54a8-47e9-b7fb-15903f145c44