MIPS: port Remove the fcontext field from all contexts.

MIPS: port Remove the fcontext field from all contexts.

Ported 8452 (8a2a360)

Original commit message:
Before: every context cached the nearest enclosing function context. This
assumed that for nested contexts (i.e., with and catch contexts) the
enclosing function had a materialized link in the context chain.
Now: when necessary, we loop up the context chain to find such a context.
This enables catch contexts without forcing the enclosing function to
allocate its own context.

BUG=
TEST=

Review URL: http://codereview.chromium.org/7284025

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8477 ce2b1a6d-e550-0410-aec6-3dcde31c8c00