disallow void in variant

...logy/matching/GeneralizedLevenshteinMatchingAutomaton.cpp

...gology/matching/GeneralizedLevenshteinMatchingAutomaton.h

...ching/GeneralizedLevenshteinSequenceMatchingAutomaton.cpp

...atching/GeneralizedLevenshteinSequenceMatchingAutomaton.h

...src/stringology/matching/LevenshteinMatchingAutomaton.cpp

...o/src/stringology/matching/LevenshteinMatchingAutomaton.h

...ngology/matching/LevenshteinSequenceMatchingAutomaton.cpp

...ringology/matching/LevenshteinSequenceMatchingAutomaton.h

.../matching/GeneralizedLevenshteinMatchingAutomatonTest.cpp

...g/GeneralizedLevenshteinSequenceMatchingAutomatonTest.cpp

...stringology/matching/LevenshteinMatchingAutomatonTest.cpp

...ogy/matching/LevenshteinSequenceMatchingAutomatonTest.cpp

alib2data/src/common/DefaultEpsilonType.h

alib2data/test-src/automaton/AutomatonTest.cpp

alib2std/src/extensions/container/variant.hpp

alib2std/test-src/extensions/container/VariantTest.cpp

alib2str/src/object/string/AnyObject.cpp

alib2xml/src/container/xml/ObjectsVariant.h