Some problems for the iphone project files after the gsoc merges

hi all,
i identified some problems compiling the SDL library for iphone in the
latest revision.

SDL_shape.h is not found by several files, i resolved it by putting
the include folder in the header search path (but maybe it’s not the
optimal way)
sdl_atan2 create a link error, it’s only because HAVE_ATAN and
HAVE_ATAN2 defines are missing from the config_iphoneos.h is broken as it tries to load a MainWindow.nib that is
non-existant; i have no fix for this one, but i’m sure that supplying
MainWindow is absolutely non mandatory.

hope this helps (and gets fixed :wink: )