[ clean ] Removed commented out code in Reduce.
[ clean ] Removed unused reduceDef.
[ refactor ] dontUnfold instead of delayed and nonterminating in Reduce.

Information whether s.th. is delayed or non-terminating is only used in
the decision whether to unfold a definition during reduction.
[ refactor ] Made an auxiliary function local.
[ refactor ] Lens for allowedReductions.

And removed two unused functions.
[ new ] functions for AssocList
[ new ] Syntax.Abstract.Name.qualify_
[ refactor ] AssocList.mapWithKeyM for Applicative m.

'Monadic' list updates are really 'Applicative'!
[ issue 1266 ] test cases moved to fail

Shadowing a local now leads to an error.
[ issue 1266 ] Changed fix to give error when referring to shadowed local.

LocalVars is not a map from concrete names to either an abstract name or
some information that this local has been shadowed by later imports.
Looking up such a shadowed local gives an error.
[ issue 1266 ] Change of scoping rules documented in CHANGELOG.