function extractInteger(buf, bufPos) {
	        var x = buf[bufPos + 0] & 0xff;
	        x <<= 8;
	        x |= buf[bufPos + 1] & 0xff;
	        x <<= 8;
	        x |= buf[bufPos + 2] & 0xff;
	        x <<= 8;
	        x |= buf[bufPos + 3] & 0xff;
	        return x;
	    }
Read big endian integer (4-bytes) from header.

@param buf
           header containing the integer
@param bufPos
           offset into the header
@return extracted integer