[BUGFIX] Fix lookup path for ``AvailableProxyClasses.php``
[BUGFIX] Fix lookup path for ``AvailableProxyClasses.php``

Since 2787b2a3216deb188c4cd1c9b2b823e6e3a10da3 Flow creates a
map for available proxy classes stored in ````AvailableProxyClasses.php``
within the temporary directory.

The ``ClassLoader`` failed to include that file though when run in
a nested Application Context. That is fixed with this change.

chewbakartik/flow-development-collection,aertmann/flow-development-collection,kdambekalns/flow-development-collection,kdambekalns/flow-development-collection,dlubitz/flow-development-collection,chewbakartik/flow-development-collection,aertmann/flow-development-collection,dfeyer/flow-development-collection,robertlemke/flow-development-collection,dfeyer/flow-development-collection,robertlemke/flow-development-collection,kdambekalns/flow-development-collection,mkeitsch/flow-development-collection,bwaidelich/flow-development-collection,fcool/flow-development-collection,kdambekalns/flow-development-collection,bwaidelich/flow-development-collection,mkeitsch/flow-development-collection,neos/flow-development-collection,dlubitz/flow-development-collection,gerhard-boden/flow-development-collection,daniellienert/flow-development-collection,kitsunet/flow-development-collection,robertlemke/flow-development-collection,robertlemke/flow-development-collection,dfeyer/flow-development-collection,kitsunet/flow-development-collection,chewbakartik/flow-development-collection,albe/flow-development-collection,neos/flow-development-collection,dfeyer/flow-development-collection,bwaidelich/flow-development-collection,kitsunet/flow-development-collection,neos/flow-development-collection,gerhard-boden/flow-development-collection,albe/flow-development-collection,fcool/flow-development-collection,albe/flow-development-collection,gerhard-boden/flow-development-collection,daniellienert/flow-development-collection,fcool/flow-development-collection,aertmann/flow-development-collection,daniellienert/flow-development-collection,mkeitsch/flow-development-collection,fcool/flow-development-collection,neos/flow-development-collection,dlubitz/flow-development-collection