some tests use signed long instead of int32_t causing issues on 64-bit systems

[giuliomoro]

Idioms such as:

typedef long int MY_TYPE;
#define FORMAT RTAUDIO_SINT32

become problematic on 64-bit systems, or more in general wherever long int is not 32 bits.

There are two instances of this in tests/duplex.cpp and tests/playsaw.cpp and tests/record.cpp, but they were commented out, so wouldn't get caught by tests. Other tests use signed int instead which may be OK, but I'd suggest to have all the types be explicit using fixed-width integers from stdint.h.