Iostreams: Fix gzip test failures in C++0x gcc 4.4.
Was getting this error:
gzip_test.cpp: In function 'void header_test()':
gzip_test.cpp:134: error: narrowing conversion of '139' from 'const int' to 'const char' inside { }
gzip_test.cpp:134: error: narrowing conversion of '156' from 'int' to 'const char' inside { }
gzip_test.cpp:134: error: narrowing conversion of '243' from 'int' to 'const char' inside { }
Although it's only a warning in later versions of gcc.