GitLab

Bind `M-s c' to `isearch-toggle-case-fold'.
(search-map): Bind `M-s _' to `isearch-forward-symbol'.
(isearch-forward): Add `M-s _' to the docstring.
(isearch-forward-symbol, isearch-toggle-case-fold)
(isearch-symbol-regexp): New functions.

Fixes: debbugs:11381