Improvement to --optional doctests

[jdemeyer]

1. Clearly document and test that --optional tags and options are case-insensitive.
2. --show-skipped never mentions skipped sage tests.
3. Check for invalid --optional arguments (basically, anything that isn't alphanumeric).

CC: @simon-king-jena

Component: doctest framework

Author: Jeroen Demeyer

Reviewer: Volker Braun

Merged: sage-5.9.rc1

Issue created by migration from https://trac.sagemath.org/ticket/14495

[jhpalmieri]

comment:2

In the developer's guide, in conventions.rst, it says

      Any words after ``# optional`` are
      interpreted as a list of package names, separated by spaces.
      Any punctuation (periods, commas, hyphens, semicolons, ...)
      after the first word ends the list of packages.
      Hyphens or colons between the word ``optional`` and the first
      package name are allowed.
      Also, all text is converted to lower case.

So the case-insensitivity is mentioned, but could be emphasized more.

[jdemeyer]

comment:3

Please review.

[jdemeyer]

Author: Jeroen Demeyer

[jdemeyer]

Attachment: 14495_optional_doctests.patch.gz

[jdemeyer]

comment:4

Given that I would prefer to merge this in sage-5.9.rc1, I appreciate a quick review :-)

[vbraun]

comment:5

Looks good to me

[vbraun]

Reviewer: Volker Braun

[jdemeyer]

Merged: sage-5.9.rc1