Add tests for ceylon/ceylon-spec#869
document divided
Add more tests for ceylon/ceylon-spec#869

Suggested by @chochos [1]. I added another test to verify that
conditions after a false condition are not evaluated:
    if (false) if (functionWithSideEffects()) value
should not have side effects.

[1]
https://github.com/lucaswerkmeister/ceylon.language/commit/f8ef15cc944987f78654ce1121187f820fcee08d#commitcomment-5126747
minor
doc for printStackTrace()
javadoc
fix toString()
fix production of union/intersection types
optimize Singleton.chain()
ws
more efficient following() for sequences
String.following in js
Fix #399 add timesInteger() and plusInteger() to Scalar
initial removal of Cloneable, LazyList, LazySet, LazyMap, UniqueElements
make tests compile
add defaulted type parameter to Category
refine clone()
remove obsolete method
Make Invertable an abstraction for groups
remove arrays from java.lang