[PATCH 0/4] MR6577: Cmd engine rewrite (part XXVI)

[eric pouech (＠epo)]

This is part XXVI of cmd engine rewrite.

It mainly tackles which variable name (single letter) are supported as FOR
loop variables.
We recently extended the scope of letters (a-z, A-Z) with digits (0-9).
A couple of bug reports show that more are supported.
More manual testing show that all 7bit ASCII characters are supported
(except the ones handled by lexer like CR, LR, \0, <SPACE>, <TAB>,
ctrl-Z...).

This serie:
- add a couple of new tests for FOR loop variables (also testing limits
  on tokens= options for setting at once several contiguous variables)
- fix all exhibited bugs
- rewrite parsing and handling of tokens= option (simplicity, correctness).