[m-dev.] for review: update WORK_IN_PROGRESS file

[Simon Taylor]

> WORK_IN_PROGRESS:
> 	- mention the support for aliasing, accumulator introduction,
> 	  and specialization of polymorphic procedures (these are
> 	  all committed onto the alias branch)

Specialization of polymorphic procedures was committed on the main branch.
It's mentioned in the NEWS file. Maybe you meant user-guided/inter-module
specialization of polymorphic procedures?

The Aditi interface should probably be mentioned somewhere in WORK_IN_PROGRESS.

Simon.