CXBMCTinyXML: use fast direct file reading

This is a future improvement of #1301, now with some numbers:

Some test:
original code, 1126 KB XML file, 5 times "create object, open file":
6001 milliseconds
5573 milliseconds
6613 milliseconds
5746 milliseconds
5589 milliseconds
5032 milliseconds
6703 milliseconds
5511 milliseconds
5739 milliseconds
5950 milliseconds
6388 milliseconds
6011 milliseconds

patched code,1126 KB XML file, 5 times "create object, open file":
2528 milliseconds
2065 milliseconds
2086 milliseconds
2423 milliseconds
2122 milliseconds
2490 milliseconds
2122 milliseconds
1875 milliseconds
1897 milliseconds
2074 milliseconds
1935 milliseconds
1859 milliseconds
2051 milliseconds
**Patched code is faster by 60-70%.**

original code, 516 B XML file, 10000 times "create object, open file":
7605 milliseconds
5874 milliseconds
7998 milliseconds
7590 milliseconds
8030 milliseconds
8388 milliseconds
5789 milliseconds
7849 milliseconds
7455 milliseconds
5951 milliseconds
7691 milliseconds

patched code, 516 B XML file, 10000 times "create object, open file":
3511 milliseconds
3058 milliseconds
3116 milliseconds
3044 milliseconds
3034 milliseconds
3052 milliseconds
3033 milliseconds
3265 milliseconds
2935 milliseconds
2894 milliseconds
2919 milliseconds
2909 milliseconds
2934 milliseconds
**So on small files we save about 50-60%.**