Switch to using Python ternary op

[mwichmann]

Python 2.5 introduced a better approach than c and x or y which is less error-prone, and, these days, and presumably more familiar to readers, as for the last 20 years Python programmers probably won't have been taught the and/or form.

For the most part this is behind the scenes - tools, tests, framework. It rises to visibility if someone looks hard at a few construction variables which now use the new form: _SHLIBVERSION, PCHPDBFLAGS, CCPDBFLAGS. There is no behavioral change even in those cases.

Contributor Checklist:

• I have created a new test or updated the unit tests to cover the new/changed functionality.
• I have updated CHANGES.txt and RELEASE.txt (and read the README.rst).
• I have updated the appropriate documentation