Issue 1451 Patch - Indexes and aliases can now work together

I corrected the bug signaled in issue 1451 (http://code.google.com/p/libgdx/issues/detail?id=1451).

In fact, only the name was stored to remember aliases while the index was also necessary.
I decided to create a new type but to let the code almost the same by overwriting the current rect.index by its aliases indexes. This may be bad if someone decide to use the "rect" variable after the "for".

Also, it will have only a very tiny impact on the running time of the TexturePacker2 tool.