Add extra debugging messages for syntax failures in yang-model-validator

java -Xmx8192m -jar ../yangtools/yang/yang-model-validator/target/yang-model-validator-5.0.0-SNAPSHOT-jar-with-dependencies.jar -p ./ -r -d vendor/cisco/xr/601/cisco-openconfig-if-aggregate-devs.yang
12:59:27.732 [main] INFO org.opendaylight.yangtools.yang.validator.Main - Yang model dirs: [./]
12:59:27.734 [main] INFO org.opendaylight.yangtools.yang.validator.Main - Yang model files: [vendor/cisco/xr/601/cisco-openconfig-if-aggregate-devs.yang]
12:59:27.734 [main] INFO org.opendaylight.yangtools.yang.validator.Main - Supported features: null
12:59:27.735 [main] INFO org.opendaylight.yangtools.yang.validator.Main - Memory INFO [start]: free 250MB, used 5MB, total 256MB, max 8192MB
12:59:27.956 [main] DEBUG org.opendaylight.yangtools.yang.parser.spi.meta.StatementSupportBundle$Builder - Changed statement (urn:ietf:params:xml:ns:yang:yin:1)anyxml support from org.opendaylight.yangtools.yang.parser.rfc7950.stmt.anyxml.AnyxmlStatementSupport@60f00693 to org.opendaylight.yangtools.yang.parser.rfc7950.stmt.anyxml.AnyxmlStatementSupport@60f00693
13:00:38.385 [main] ERROR org.opendaylight.yangtools.yang.validator.Main - Failed to create SchemaContext.
org.opendaylight.yangtools.yang.model.parser.api.YangSyntaxErrorException: no viable alternative at input '\n       ;'
	at org.opendaylight.yangtools.yang.parser.rfc7950.repo.YangErrorListener.syntaxError(YangErrorListener.java:42)
	at org.antlr.v4.runtime.ProxyErrorListener.syntaxError(ProxyErrorListener.java:41)
	at org.antlr.v4.runtime.Parser.notifyErrorListeners(Parser.java:544)
	at org.antlr.v4.runtime.DefaultErrorStrategy.reportNoViableAlternative(DefaultErrorStrategy.java:310)
	at org.antlr.v4.runtime.DefaultErrorStrategy.reportError(DefaultErrorStrategy.java:136)
	at org.opendaylight.yangtools.yang.parser.antlr.YangStatementParser.statement(YangStatementParser.java:294)
	at org.opendaylight.yangtools.yang.parser.antlr.YangStatementParser.statement(YangStatementParser.java:229)
	at org.opendaylight.yangtools.yang.parser.antlr.YangStatementParser.statement(YangStatementParser.java:229)
	at org.opendaylight.yangtools.yang.parser.rfc7950.repo.YangStatementStreamSource.parseYangSource(YangStatementStreamSource.java:171)
	at org.opendaylight.yangtools.yang.parser.rfc7950.repo.YangStatementStreamSource.create(YangStatementStreamSource.java:98)
	at org.opendaylight.yangtools.yang.parser.impl.YangParserImpl.sourceToStatementStream(YangParserImpl.java:119)
	at org.opendaylight.yangtools.yang.parser.impl.YangParserImpl.addLibSource(YangParserImpl.java:73)
	at org.opendaylight.yangtools.yang.validator.SystemTestUtils.parseYangSources(SystemTestUtils.java:103)
	at org.opendaylight.yangtools.yang.validator.SystemTestUtils.parseYangSources(SystemTestUtils.java:87)
	at org.opendaylight.yangtools.yang.validator.Main.runSystemTest(Main.java:177)
	at org.opendaylight.yangtools.yang.validator.Main.main(Main.java:136)
Caused by: org.antlr.v4.runtime.NoViableAltException: null
	at org.antlr.v4.runtime.atn.ParserATNSimulator.noViableAlt(ParserATNSimulator.java:2026)
	at org.antlr.v4.runtime.atn.ParserATNSimulator.execATN(ParserATNSimulator.java:467)
	at org.antlr.v4.runtime.atn.ParserATNSimulator.adaptivePredict(ParserATNSimulator.java:393)
	at org.opendaylight.yangtools.yang.parser.antlr.YangStatementParser.statement(YangStatementParser.java:207)
	... 10 common frames omitted
░▒▓    ~/repos/OpenDaylight/yang    master +2 !25 ?1 ▓▒░