file seek support, new test cases, AVI use file seek

ext/sd/fat32/File.h

@@ -32,6 +32,16 @@ public:
 	std::string getName() const {return h.getName();}
 
 
+	/** current position within the file */
+	uint32_t curPos() const {
+		return curAbsPos;
+	}
+
+	/** seek to a new position within the file */
+	void seekTo(uint32_t pos) {
+		_seekTo(pos);
+	}
+
 	/** read x bytes from the file */
 	uint32_t read(uint32_t size, uint8_t* dst) {
 
@@ -105,6 +115,12 @@ private:
 
 	}
 
+	void _seekTo(uint32_t pos) {
+		this->curAbsPos = pos;
+		this->iCurCluster = pos / fs.tmp.bytesPerCluster;
+		this->posInCluster = pos - (this->iCurCluster * fs.tmp.bytesPerCluster);
+	}
+
 	int32_t _read(uint32_t readSize, uint8_t* dst) {
 
 		// EOF reached?