Introduce MODtoChars to avoid code duplication.
Fixes Issue 9368 - Final switch on typedef'ed enum is not properly checked
Fix issue 1841 Closure detection fails in nested functions

If an escaping function doesn't use any closure variables, but
calls another nested function which does, it must be marked as
needing a closure. This 'calling a sibling' case was missing.
fix Issue 9409 - [2.062-alpha] Regression with $ inside of expression tuples
more simplifying backend interface
Using rsp instead of esp

See http://forum.dlang.org/thread/jythfvgxrvqvdphaihlr@forum.dlang.org and https://github.com/ldc-developers/ldc/pull/269.
small cleanup
Merge pull request #1546 from AndrejMitrovic/RefactorMod

Introduce MODtoChars to avoid code duplication.
Merge pull request #1554 from donc/closure1841

1841 Closure detection fails in nested functions
Merge pull request #1563 from WalterBright/b36

more simplifying backend interface
Merge pull request #1564 from sgraf812/patch-1

Using rsp instead of esp
Merge pull request #1562 from 9rnsr/fix9409

Issue 9409 - [2.062-alpha] Regression with $ inside of expression tuples
more type refactoring
Merge pull request #1565 from WalterBright/b37

more type refactoring
move slist to back end
Merge pull request #1566 from WalterBright/b38

move slist to back end
refactor type_function
Merge pull request #1567 from WalterBright/b39

refactor type_function
Merge pull request #1534 from AndrejMitrovic/Fix9368

Issue 9368 - Final switch on typedef'ed enum is not properly checked