adapt regexps to new visitor technique

alib2algo/src/regexp/convert/ToAutomatonThompson.cpp

alib2algo/src/regexp/convert/ToAutomatonThompson.h

alib2algo/src/regexp/properties/RegExpEmpty.cpp

alib2algo/src/regexp/properties/RegExpEmpty.h

alib2algo/src/regexp/properties/RegExpEpsilon.cpp

alib2algo/src/regexp/properties/RegExpEpsilon.h

alib2algo/src/regexp/transform/RegExpDerivation.cpp

alib2algo/src/regexp/transform/RegExpDerivation.h

alib2algo/src/regexp/transform/RegExpIntegral.cpp

alib2algo/src/regexp/transform/RegExpIntegral.h

alib2data/src/regexp/common/RegExpToXMLComposer.cpp

alib2data/src/regexp/common/RegExpToXMLComposer.h

alib2data/src/regexp/formal/FormalRegExpAlternation.h

alib2data/src/regexp/formal/FormalRegExpConcatenation.h

alib2data/src/regexp/formal/FormalRegExpElement.h

alib2data/src/regexp/formal/FormalRegExpEmpty.h

alib2data/src/regexp/formal/FormalRegExpEpsilon.h

alib2data/src/regexp/formal/FormalRegExpIteration.h

alib2data/src/regexp/formal/FormalRegExpStructure.cpp

alib2data/src/regexp/formal/FormalRegExpSymbol.h