When we check two type objects equality, we should use Type::equals instead of directly pointer comparison.
Default args and arg identifiers are now volatile information in TypeFunction.

1. The extra informations would be kept after semantic analysis for function pointer and delegate types. But merging type would strip all the extras from the type structure, then cache the stripped copy into.

2. The types has extra informations cannot be named. In other words, AliasDeclaration would always strip the aliased type. This rule also works for Template Type Parameter, and fixes issue 3646 well.

3. CondExp would strip them from the type of its result.
Improved fix for Issue 3866 - anonymous delegate with default parameters cross-talks to another anonymous delegate

This reverts commit acc22ce25db42facfe4917aeceabd28a410f4c95,
and moves original test into runnable/functype.d
fix Issue 3646 - Default values of function arguments are ignored when instantiating a template.
fix Issue 8579 - Default parameter appears a part of typeof().stringof of a function variable
Fix CppMangle issue

Use merge2() result for function argument types mangling.
Merge pull request #1102 from 9rnsr/improveDefArgs

Improve default argument processing
fix issue 10542 - implicitly generated class ctor doesnt inherit base
class ctor attributes
Merge pull request #2297 from hpohl/10542

fix issue 10542 - implicitly generated class ctor doesn't inherit base class ctor attributes
Issue 10539 - Implicit pointer to array dereference for .ptr property fails
Merge pull request #2296 from 9rnsr/fix10539

[REG2.063] Issue 10539 - Implicit pointer to array dereference for .ptr property fails
fix Issue 10537 - Forward reference error on 'yield' toy example.
Merge pull request #2298 from 9rnsr/fix10537

[REG2.063] Issue 10537 - Forward reference error on 'yield' toy example.