Change sampleCount arguments, variables, return values to size_t...

... whenever they really describe the size of a buffer that fits in memory, or
of a block file (which is never now more than a megabyte and so could be fit in
memory all at once), or a part thereof.

src/effects/EffectManager.h

@@ -108,7 +108,7 @@ public:
    void RealtimeSuspend();
    void RealtimeResume();
    void RealtimeProcessStart();
-   sampleCount RealtimeProcess(int group, unsigned chans, float **buffers, sampleCount numSamples);
+   size_t RealtimeProcess(int group, unsigned chans, float **buffers, size_t numSamples);
    void RealtimeProcessEnd();
    int GetRealtimeLatency();