STL include file guard names

[Benjamin Kosnik]

>Is there a reason for the change? It seems to me that the 3.3.3 style 
>has the benefit of being much less likely to clash with other libraries.

There were a mix of include guard names pre 3.4. I attempted to
standardize all the guard names in all the include files, using the
shortest possible names based on libc style. Perhaps this wasn't
optional, but I am unaware of actual problems posed by the new names.

-benjamin