assignVar helper does not work with SafeString

[peterrakmanyi]

1. All the helpers with a string output actually return a SafeString object.
2. Not all helpers that accept a string input work with SafeString.

• custom helper: {{assignVar "foo" (concat "b" "ar")}} results in error:
  assignVar helper value must be a string or a number (integer)

• standard helper: {{trim (concat "b" "ar")}} fails to default "" empty string

3. There is no helper to get a string from SafeString.

[peterrakmanyi]

It appears that there is a workaround with using the get helper like this:
{{get 'string' (concat "b" "ar")}} results in "bar"

...

{{assignVar "foo" (get 'string' (concat "b" "ar"))}} does result in var foo="bar"