[jbigot]

DISABLE_PDI is a very generic a name for a cache variable: any project that adds the example, the distribution among them, may own a variable of that name. The switch that builds the example against the mock PDI is renamed PDI_EXAMPLE_USE_MOCK_PDI, after the project it belongs to, and the documentation that uses it as the model of a SubdirMock setup follows.

Fix #785

List of things to check before making a PR

Before merging your code, please check the following:

• you have added a line describing your changes to the Changelog;
• you have checked your code format:
  • you have checked that you respect all conventions specified in CONTRIBUTING.md;
• you have correctly updated the copyright headers:
  • your institution is in the copyright header of every file you (substantially) modified;
  • you have checked that the end-year of the copyright there is the current one;
• you have updated the AUTHORS file:
  • you have added yourself to the AUTHORS file;
  • if this is a new contribution, you have added it to the AUTHORS file;
• you have added everything to the user documentation:
  • any other new or changed user-facing feature;
• you have correctly linked your PR to one or more issues:
  • your PR solves an identified issue;
  • your commit contain the Fix #issue keyword to autoclose the issue when merged.

[jmorice91]

I suggest a little change in the variable name to improve the understanding and the reusing of the users.

When we are agree with the new name, this PR is ready to ship.