Fix complain about uint32_t and uint16_t already defined in /usr/include/stdint.h. Happens on Debian Etch.

Error text:

filecontainerzip.cpp: In member function 'virtual bool synfig::FileContainerZip::open(const std::string&)':
filecontainerzip.cpp:315: error: reference to 'uint16_t' is ambiguous
/usr/include/stdint.h:50: error: candidates are: typedef short unsigned int uint16_t
...
filecontainerzip.cpp:427: error: reference to 'uint32_t' is ambiguous
/usr/include/stdint.h:52: error: candidates are: typedef unsigned int uint32_t
filecontainerzip.cpp:55: error:                 typedef unsigned int synfig::FileContainerZip_InternalStructs::uint32_t