Fix for issue 1995.

Fix for issue 1995.

This changes containg a fix for Issue 1995.
When remorphing an argument that has been already completed (in case of
CSE rewriting for example, as in this case) the classification code was
not run properly and it is triggering an assertion. As the Issue 1995
states the assert failure is benign since the generated code is correct -
the change of registers used during completed argument classification is
not allowed and the code is not changing them.
This changes add the necessary code to properly classify and assign
registes for completed arguments remorphing, which complies with the expectations of the failing assert.