Incorrect group optimizing if stroke="none"

[launchpad-issue-importer]

For example a stroke="none" declaration get removed in the optimization, then sometimes the objects get a stroke if there is a upper-group with stroke="#...".

For practical example see this version from User:Palosirkka: http://commons.wikimedia.org/wiki/File:Dialog-warning.svg

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Imported from Launchpad using lp2gh.

• date created: 2012-09-14T21:12:21Z
• owner: groby999
• the launchpad url was https://bugs.launchpad.net/bugs/1051079

[Ede123]

Duplicate of #22