Attachment tests (cf #245)

@springmeyer: Here is one first shot, only for "internal" attachments (inside one symbolizer).
Tell me if it's useful.
I can do the same kind of "basic tests" for external attachments and order if you want.
And if you have specific ideas of thing to tests, push me a line :)

Going for a walk now, but will be back online in one hour or so.

Yohan