[nem-en] Integration again

[vc]

> Could you (or Igor) please explain how and when do you save TExpr? Or
> point me to the place in the code where it happens?

* In ctor of MethodBuilder
(http://nemerle.org/svn/nemerle/trunk/ncc/hierarchy/ClassMembers.n line
1091) we safe tokens of method body to _bodyTokens.
* Method ResetBody() (line 768) reset it field and other field (_bodyParsed
and _bodyTyped).
* Property BodyTokens check _bodyTokens and return it content or tokenize
source.
* Property BodyParsed (line 811) check _bodyParsed and return it content or
parse tokens (from BodyTokens) to PExpr.
* Property BodyTyped (line 835) check _bodyTyped and return it content or
call RunBodyTyper() for type body.

We trace changes in file and if body of some method is changed we call
ResetBody(). It reset all fields which cache the method AST. In next time
BodyTokens, BodyParsed and BodyTyped reparse and retype method body.