Make class `this` and `super` rvalues.
Update test case diagnostic output.
Add test for this fix.
fix Issue 13252 - ParameterDefaultValueTuple affects other instantiations

Expression::equals should also compare operand types.
fix Issue 13259 - [ICE] 'v.result' on line 191 in file 'todt.c'
Merge pull request #3761 from quickfur/issue13116

Issue 13116: should reject returning `this` from a ref class member function
Remove toHeadMutable call from NullExp::equals and ArrayLiteralExp::equals

I'm not sure we should also remove toHeadMutable call from IntergerExp, RealExp, ComplexExp, and VarExp::equals. To avoid accidental existing code breaking, I'd leave them in 2.066 beta/rc phase.
Merge pull request #3847 from 9rnsr/fix13259

[REG2.066a] Issue 13259 - [ICE] 'v.result' on line 191 in file 'todt.c'
Merge pull request #3846 from 9rnsr/fix13252

[REG2.061] Issue 13252 - ParameterDefaultValueTuple affects other instantiations