Add the childExists method.
Always rewind the grammar while getting the AST.
[auto] Merge from Compiler

    • #dfa21ea — Add the childExists method. (Ivan Enderlin, 2013-06-24)
    • #bfa6989 — Always rewind the grammar while getting the AST. (Ivan Enderlin, 2013-06-24)

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Merge remote branch 'library-compiler/master'