Revert "Xcode project file: fix user data directory name"

This reverts commit 3b457ab9900d920e21e15dbc36cc55eb091fc210.
Revert "Xcode project: switch to using the new boost filesystem code"

This reverts commit 3d906be9ee4c283d234ac2bfa652bf4c3b71f195.
Revert "Xcode project: add 'Runpath Search Path" for wesnothd"

This reverts commit b228f0002a20e770e4345ca64d6f47a8fb45c2f6.
Revert "Xcode project: update boost and SDL libraries"

This reverts commit 7199486105ab6c404f60578ceb338d72dcc98f4d.
Xcode project: revert to the old filesystem code for Apple OS X

This is for compatibility with OS X 10.5 only, with newer version of OS
X the new boost filesystem code works just fine.
Add a missing include for Apple OS X