Correctly deal with invalid content in non-selfclosing tags. Fixes #297
Add test for #197. Fixes #197
layer srs is inherited from map srs

Do not output srs attribute when srs is undefined,
since layer srs is inherited from map srs, it is optional.
Add test for #294
Integrate mml parsing test for issue #297
Merge pull request #300 from strk/master-invalid-non-selfclosing-mml

Integrate mml parsing test for issue #297
Merge pull request #294 from kapouer/patch-1

layer srs is inherited from map srs
bump mapnik-reference version and prep changelog for v0.9.5 release
Fix empty name value resulting in non closed tag
Merge pull request #305 from yohanboniface/empty_name_invalid_xml

Fix empty name value resulting in non closed tag
drain millstone pool forcefully so we can exit quickly - refs #301 and mapbox/millstone#110
checks for millstone.drainpool only if -l flag is passed
Merge pull request #306 from dboze/fix-drainpool

check for millstone.drainpool only if -l flag is passed
fix direct-image-filters output and add test for image-filters
track latest mapnik-reference
Filter key=null cannot merge with other operators