DOCBOOK: docbook-xsl: has.ext doesn't work with relative paths...

see at common.xsl of docbook-xsl

 <xsl:variable name="has.ext" select="contains($filename, '.') != ''"/>

this doesn't work when filename="../test" suppose test.png is the file...

suggest: exists functions that strips beginning relative paths or strips out 
all characters until last slash /, and then apply to this the contains, 
function ?