support saving exogenous variables in `dynasave`, `dynasave`; fix bugs in `dynasave`; add test

- `dynasave`: if a variable being saved was named `n` or `s`, the `eval` statements would break the code
- `dynasave`: use the `-struct` option to `save` to avoid `eval` statements
- `dynasave` and `dynatype`: do everything in 1 loop instead of 2
- `dynasave` and `dynatype`: use `strcmp` instead of `strfind`

- preprocessor update contains:
  - Allow `dynasave` and `dynatype` to support exogenous variables in their var_list

issue #1691

(cherry picked from commit bf102030)