Merge : re-applies missing part of fix for Bug 2901,Add export for s60ibymacros.pm
By default, .mmp files that include FEATUREVARIANT will generate binaries for
both "normal", non-binary variant, build configurations and binary variant
build configurations.
In order to ensure that only invariant binaries are created for invariant
build configurations, and variant binaries for variant build configurations,
the optional setting FEATUREVARIANTSAFE can be used. FEATUREVARIANTSAFE can be
set via an os_properties.xml file and, when set, variant binaries will no
longer be created for invariant build configurations.