Rejigger some FIFO buffer variables to be more rational.

videoBuffer -> s_video_buffer
size -> s_video_buffer_write_ptr
g_pVideoData -> g_video_buffer_read_ptr (impl moved to Fifo.cpp)

This eradicates the wonderful use of 'size' as a global name, and makes
it clear that s_video_buffer_write_ptr and g_video_buffer_read_ptr are
the two ends of the FIFO buffer s_video_buffer.

Oh, and remove a useless namespace {}.

Source/UnitTests/VideoCommon/VertexLoaderTest.cpp

@@ -74,7 +74,7 @@ protected:
 
 	void ResetPointers()
 	{
-		g_pVideoData = &input_memory[0];
+		g_video_buffer_read_ptr = &input_memory[0];
 		VertexManager::s_pCurBufferPointer = &output_memory[0];
 		m_input_pos = m_output_pos = 0;
 	}