fix Issue 9374 - 'super' should be accessible inside template constraint
fix Issue 6538 - ICE(mangle.c) Invalid template constraints
fix Issue 9361 - Nasty bug and/or error message for template constaints using this

Add test cases
Merge pull request #1539 from 9rnsr/fix6538

Issue 6538 - ICE(mangle.c) Invalid template constraints