Issue #259: fix `ProjectDefinition >> classesForPlatform` and use it `#testSuite`
THis allows packages to specify testcases valid for some platform only.
This is normally not needed but sometimes the testcase uses a class
that is platform specific and this will cause package validation
error upon commit.
This directory contains (what we consider) fundamental
classes required for any serious Smalltalk application
(both headless and GUI-based).
Of course, for special applications, even this set of
classes could be reduced
(for smaller apps, some of LargeInteger, Float, Fraction
etc. could be left out).
We do not provide tools or support for such minimal
configurations - with modern, paged OperatingSystems, there
is also less sense in doing so, since unused code is simply
paged out or never paged in at all.