[Patch, Fortran] Fix MOVE_ALLOC check

[Tobias Burnus]

This patches fixes my previous MOVE_ALLOC patch. The standard states for 
TO: "It shall be polymorphic if FROM is polymorphic."

I somehow read this bijectively, but the it is actually allowed to have 
a nonpolymorphic FROM with a polymorphic TO. Thanks for Damian for 
finding this.

Build and regtested on x86-64-linux.
OK for the trunk?

Tobias

PS: Other pending patches:
- http://gcc.gnu.org/ml/fortran/2011-11/msg00249.html - Pointer 
INTENT(IN) check for MOVE_ALLOC [4.6/4.7 rejects-valid regression]
- http://gcc.gnu.org/ml/fortran/2011-11/msg00250.html - no 
-fcheck=bounds for character(LEN=:) to avoid ICE
- http://gcc.gnu.org/ml/fortran/2011-11/msg00253.html - (Re)enable 
warning if a function result variable is not set [4.4-4.7 diagnostics 
regression]
- http://gcc.gnu.org/ml/fortran/2011-11/msg00254.html - Thomas' 
dependency-ICE patch [4.6/4.7 regression]
- http://gcc.gnu.org/ml/fortran/2011-12/msg00005.html - Fix 
component-access check
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