Normalize comma-escaping of src-blocks and example-blocks
* lisp/org-src.el (org-escape-code-in-string,
org-unescape-code-in-string, org-escape-code-in-region,
org-unescape-code-in-region): New functions.
(org-edit-src-code, org-edit-src-exit): Use new functions.
* lisp/org.el (org-strip-protective-commas): Removed function.
* lisp/org-exp.el (org-export-select-backend-specific-text): Use new
function.
* lisp/ob.el (org-babel-parse-src-block-match,
org-babel-parse-inline-src-block-match, org-babel-insert-result):
Always escape produced blocks, independently on the language of the
block, if any. Use new functions.
* doc/org.texi: Update documentation.
* testing/lisp/test-ob.el: Update test.