Getters and setters for Long preference values

[theSlyest]

I needed to store Long values for my game, so I added the getter and setter methods for each supported platform. In fact, I should have done this earlier, since I made these changes when I was using version 3.17.

[halx99]

Actually, I don't recommend use Long, for cross-platform game engine, use integer type with explicit word size is better, such as int32_t, int64_t

The type long 's word size is different on win32 and non-win32 system

[halx99]

intptr_t also better than long

[theSlyest]

You are right, so I switched from long to int64_t