Tag pooling impl.

[cmanolache]

Hi Casey,

There is a small problem when building with jikes. The
TagPoolInterceptor depends on jasper runtime, which depend on the servlet
api - I think it should be moved into the facade ( for now ). We do need a
serious refactoring of jasper - and that would clarify a lot of
things. There is no problem with javac, since it doesn't use
"strict" rules. 

I'll do the move if you don't mind. I like the idea of having a general 
and facade-independent pool mechanism, but we can do that later. 

Costin