Fix Issue 5943 - Power expression optimisation: 2^^unsigned ==> 1<<unsigned
Fix issue 10397 ICE with __error in concatenation

ErrorExp was allowing implicit conversions in some cases, because
it is derived from IntegerExp! This made errors become un-errors
again in some circumstances.
Merge pull request #2230 from donc/ctfe10397__error

Regression 10397 ICE with __error in concatenation
Fix copy-paste bug in interpret
Merge pull request #1498 from yebblies/issue5943

Fix Issue 5943 - Power expression optimisation: 2^^unsigned ==> 1<<unsigned
Merge pull request #2232 from yebblies/ctfeconv

[DDMD] [REG] Fix copy-paste bug in interpret