new gensym handling (#11985)

* new .gensym implementation
* make astspec test green again
* introduce a --useVersion switch to group compatibility switches
* fixes #10180
* fixes #11494 
* fixes #11483
* object constructor fields and named parameters are also not gensym'ed
* disabled broken package

changelog.md

@@ -10,6 +10,13 @@
   to UTF-8. Use the new switch `-d:nimDontSetUtf8CodePage` to disable this
   feature.
 
+- The language definition and compiler are now stricter about ``gensym``'ed
+  symbols in hygienic templates. See the section in the
+  [manual](https://nim-lang.org/docs/manual.html#templates-hygiene-in-templates)
+  for further details. Use the compiler switch `--useVersion:0.19` for a
+  transition period.
+
+
 ### Breaking changes in the standard library