zcert: remove code duplication
zcert: Check errors in constructor
zcert: assert constructors
zcert: assert constructors in test
zcertstore: Check errors in constructor
zcertstore: assert constructors in test
zchunk: Check constructor when creating chunk from file
zchunk: assert constructors in test
zconfig: Handle error in constructor better
zconfig: simplify destructor
zconfig: assert constructors
zconfig: assert constructors in test
zctx: simplify constructor
zctx: Remove code duplication for shadow context
zctx: check errors in test
zdigest: Check errors in constructor
zdigest: assert constructors in test
zdir: check for errors
zdir: Check errors in constructor
zdir: assert constructors in test