fix some screw-up with internal vs deck names

Parser::hasKeyword() was called with deckNames but looked up the map
for internal names. This patch renames the method to hasDeckName(),
renames Parser::getKeyword() to Parser::getKeywordFromDeckName() and
adapts/extends the tests.

opm/parser/eclipse/IntegrationTests/ParseVFPPROD.cpp

@@ -38,7 +38,7 @@ using namespace Opm;
 BOOST_AUTO_TEST_CASE( parse_VFPPROD_OK ) {
     ParserPtr parser(new Parser());
     boost::filesystem::path file("testdata/integration_tests/VFPPROD/VFPPROD1");
-    BOOST_CHECK( parser->canParseKeyword("VFPPROD"));
+    BOOST_CHECK( parser->canParseDeckKeyword("VFPPROD"));
 
     DeckPtr deck =  parser->parseFile(file.string());