Define condition variable-used-in-multiple-accumulations

[robert-strandh]

• In the file Code/Loop/compile-time-conditions.lisp, define a new condition VARIABLE-USED-IN-MULTIPLE-ACCUMULATIONS. It should have slots for the variable, and two accumulation types.

• In the file Code/Loop/condition-reporters-english.lisp, define a condition reporter, modeled after the others in the same file, specialized to the new condition type. The message should be the one that is currently in the call to ERROR in the file Code/Loop/analysis.lisp, in the function CHECK-ACCUMULATION-CATEGORIES.

• In the file Code/Loop/analysis.lisp, in the function CHECK-ACCUMULATION-CATEGORIES, replace the existing call to ERROR by a call to ERROR using the new condition.