[BUGFIX] Arrays as form objects also support property paths

When having an array as form object and a dotted property notation
for form fields, that dotted notation wasn't followed for no
reason. Now it's possible to have a ``<f:form.textfield
property="product.tag" />`` if the underlying form object is
``array('product'=>array('tag'=>'somevalue'))``.

Change-Id: I4fde16652550f37bb18cc63cefacdba7be39fde5
Releases: master, 2.2, 2.1
Merge branch 'master' of git://git.typo3.org/Packages/TYPO3.Fluid