preprocessor:

* fixed a bug with EXPECTATION operator: now handle model local variables
* substitute EXPECTATION operator even in deterministic models (for avoiding crashes, even if use of this operator doesn't make sense there)
* forbid the use of EXPECTATION and STEADY_STEATE outside model block
* minor implementation changes in EXPECTATION and STEADY_STATE operators

reference manual:
* documented EXPECTATION and STEADY_STATE operators
* added a note in write_latex_{static,dynamic}_model commands documentation about auxiliary variables and other model transformations


git-svn-id: https://www.dynare.org/svn/dynare/trunk@3145 ac1d8469-bf42-47a9-8791-bf33cf982152