ob-table: Fix org-sbe's handling of quotes in cell values
* ob-table.el (org-sbe): org-sbe did the wrong thing when given a
reference to a cell containing quotes or backslashes, because it would
simply wrap any $-prefixed value in quotes, without any escaping. Fix
this by using "%S" (instead of "\"%s\"").
* test-ob-table.el: Add test.