Fix crash in _ignore_dependency
Fix unnecessary rebuild (bug 487198)

This one was caused by a mix of >= and < dependencies.
Rename the test as requested by Sebastian to testSlotConflictMixedDependencies
Don't filter USE for binary packages with IUSE (bug 485920)

USE may contain values that aren't present in IUSE for any
supported EAPI. This for example breaks use dependencies on
USE_EXPAND-values.

The behavior for binary packages is now in line with what is
done for installed packages.

Note that this filtering was not active during merge.

URL: https://bugs.gentoo.org/485920