Fix a somewhat serious bug in the WriteString loop.

memmove was being performed on |string|, which is an NSString. The proper variable
to operate on is |cString|. But even then, that's not correct because the
destination buffer is not owned. Use pointer arithmetic instead.
Switch to using the 10.8 SDK with a 10.5 deployment target.
Rewrite NetworkCallbackController::WriteString to actually deal in bytes properly.
Delete some obsolete Xcode project settings.
Fix 64-bit Debug builds.
Replace deprecated -compositeToPoint:operation: call.
Update the comments in NetworkCallbackController::WriteString