Cffi fix

  Attached is a fix for the case when arrays are declared inside structs. For the  case:
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struct _vec3 {
  double v[3];}
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SWIG currently generates the incorrect FFI code:
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(cffi:defcstruct vec3 
   (v :pointer))
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instead of:
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(cffi:defcstruct vec3 
   (v :double :count 3))
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This patch fixes this bug.