Fix error_string() following revert to old string format

Did not realize during testing of issue #14099 that the error api had
been modified as well... reverting that change too.
Fix application error 0 in manage_config_workflow_page.php

This was due to missing type cast when calling check_checked() in
print_enum_string_option_list().

Fixes #16047
Fix #16051: spacing of selected item in bracketed menus
Rename constant UNABLE_TO_DUPLICATE -> UNABLE_TO_REPRODUCE

Old constant has been moved to a new section for deprecated constants at
the end of the file.
Move ERROR_BUG_RESOLVED_ACTION_DENIED to deprecated section
bug_update: better error message for invalid resolution

The error generated when target resolution is not valid as described in
issue #15653 is not very clear.

We now print a new, improved error message ERROR_INVALID_RESOLUTION,
which includes both the target resolution and status codes.
bug_update.php: validation for change in resolution

- Reopening an issue must not cause an error (regression introduced by
  035a1302792ada9ba36ed1d729542ea629de8cca)
- Don't reopened resolution unless old status >= RESOLVED
- fix a few other cases of invalid transitions

Fixes #15653