tokens with backslashes need to be escaped in tokens file

[robstoll]

I have defined a token as follows:

tokens{ Backslash = '\\';}

and I am reusing the resulting tokens file in another grammar like this

options{tokenVocab=OtherGrammar;}

Unfortunately, I get a NullPointerException when reusing it since the token is defined as follows in the tokens file

' \\' = 78

it should be defined as follows (then I get no NullPointerException any more):

'\\\\' = 78

Stackstrace

[13:17:57] java.lang.NullPointerException
    at org.antlr.tool.AssignTokenTypesBehavior.aliasTokenIDsAndLiterals(AssignTokenTypesBehavior.java:288)
    at org.antlr.tool.AssignTokenTypesBehavior.defineTokens(AssignTokenTypesBehavior.java:225)
    at org.antlr.tool.CompositeGrammar.assignTokenTypes(CompositeGrammar.java:347)
    at org.antlr.tool.Grammar.setGrammarContent(Grammar.java:649)
    at org.antlr.works.grammar.antlr.ANTLRGrammarEngineImpl.createNewGrammar(ANTLRGrammarEngineImpl.java:192)
    at org.antlr.works.grammar.antlr.ANTLRGrammarEngineImpl.createParserGrammar(ANTLRGrammarEngineImpl.java:225)
    at org.antlr.works.grammar.antlr.ANTLRGrammarEngineImpl.createCombinedGrammar(ANTLRGrammarEngineImpl.java:203)
    at org.antlr.works.grammar.antlr.ANTLRGrammarEngineImpl.createGrammars(ANTLRGrammarEngineImpl.java:165)
    at org.antlr.works.grammar.antlr.ANTLRGrammarEngineImpl.analyze(ANTLRGrammarEngineImpl.java:272)
    at org.antlr.works.grammar.engine.GrammarEngineImpl.analyze(GrammarEngineImpl.java:325)
    at org.antlr.works.grammar.CheckGrammar.run(CheckGrammar.java:70)
    at java.lang.Thread.run(Thread.java:745)

[sharwell]

If the following appears in a grammar:

tokens{ Backslash = '\\';}

Then the following should appear in the .tokens file:

Backslash=78
'\\'=78

According to the issue description, the tokens file generation process is working correctly.