Add fusion-bundle-target.xcconfig
Add fusion-bundle-target.xcconfig

Will use this to provide a consistent basis (in terms of build settings)
for all Fusion plug-ins.

At this stage the only setting passes "-undefined dynamic_lookup" to the
linker. This is a double-edged sword:

  - it allows us to refer to symbols in Fusion.framework without having
    to explicitly link to it at build time; so far, this is just
    laziness
  - more importantly, it allows us to refer to symbols in other plugins
    without having to link to them (and we're lucky to have this
    setting, because we couldn't link to another loadable bundle even if
    we wanted to)
  - this is less work than the alternatives of:
      - getting access to classes using NSStringFromClass()
      - defining protocols for all the "foreign" objects we wish to
        speak with and then doing all interaction by accessing instances
        with type "id <SomeProtocol>"
  - instead, we can just reference the header file of the plug-in we
    wish to speak with and proceed as though we had access to those
    classes inside our bundle
  - the down side of all this is that it can mask build errors, because
    if we make a mistake setting up the build, we won't find out about
    it until runtime; this isn't really an impediment though, because
    exactly the same kind of error-masking can occur with the
    alternative strategies using NSStringFromClass() and protocols

Signed-off-by: Wincent Colaiuta <c76ac2e9cd86441713c7dfae92c451f3e6d17fdc@wincent.com>

wincent/fusion