Fix #554 Use CMAKE_BUILD_TYPE for splash2txt

 - use CMAKE_BUILD_TYPE instead of S2T_RELEASE cmake option
 - fix a compile error with gcc 4.9 (uint32_t undefined)

Fix for #554 
There are currently actually a few boost warnings so I would vote against this :)
```
/home/felix/bin/boost_1.54/include/boost/concept_check.hpp: In destructor 'boost::ReversibleContainer<C>::~ReversibleContainer()':
/home/felix/bin/boost_1.54/include/boost/concept/detail/general.hpp:71:20: warning: typedef 'boost_concept_check731' locally defined but not used [-Wunused-local-typedefs]
       BOOST_PP_CAT(boost_concept_check,__LINE__)
                    ^
/home/felix/bin/boost_1.54/include/boost/preprocessor/cat.hpp:29:34: note: in definition of macro 'BOOST_PP_CAT_I'
 #    define BOOST_PP_CAT_I(a, b) a ## b
                                  ^
/home/felix/bin/boost_1.54/include/boost/concept/detail/general.hpp:71:7: note: in expansion of macro 'BOOST_PP_CAT'
       BOOST_PP_CAT(boost_concept_check,__LINE__)
       ^
/home/felix/bin/boost_1.54/include/boost/concept/assert.hpp:44:5: note: in expansion of macro 'BOOST_CONCEPT_ASSERT_FN'
     BOOST_CONCEPT_ASSERT_FN(void(*)ModelInParens)
     ^
/home/felix/bin/boost_1.54/include/boost/concept_check.hpp:729:11: note: in expansion of macro 'BOOST_CONCEPT_ASSERT'
           BOOST_CONCEPT_ASSERT((
           ^
/home/felix/bin/boost_1.54/include/boost/concept/detail/general.hpp:71:20: warning: typedef 'boost_concept_check733' locally defined but not used [-Wunused-local-typedefs]
       BOOST_PP_CAT(boost_concept_check,__LINE__)
                    ^
/home/felix/bin/boost_1.54/include/boost/preprocessor/cat.hpp:29:34: note: in definition of macro 'BOOST_PP_CAT_I'
 #    define BOOST_PP_CAT_I(a, b) a ## b
                                  ^
/home/felix/bin/boost_1.54/include/boost/concept/detail/general.hpp:71:7: note: in expansion of macro 'BOOST_PP_CAT'
       BOOST_PP_CAT(boost_concept_check,__LINE__)
       ^
/home/felix/bin/boost_1.54/include/boost/concept/assert.hpp:44:5: note: in expansion of macro 'BOOST_CONCEPT_ASSERT_FN'
     BOOST_CONCEPT_ASSERT_FN(void(*)ModelInParens)
     ^
/home/felix/bin/boost_1.54/include/boost/concept_check.hpp:733:11: note: in expansion of macro 'BOOST_CONCEPT_ASSERT'
           BOOST_CONCEPT_ASSERT((BidirectionalIterator<const_reverse_iterator>));
```