Fix DCD debug build

Currently DCD debug building fails as it is described in [issue 101](https://github.com/Hackerpilot/DCD/issues/101). 
It seems like assumeSorted requires opCmp operator for Token. Token itself is an alias for std.lexer.TokenStructure!(IdType, extraFields) that has opCmp(size_t i) generated by mixin extraFields (from libdparse/src/std/d/lexer.d +84) but does not have opCmp for Token. 
Actually, I don't know details of TokenStructure so I'm not sure that this operator was implemented correctly, but it fixes compilation.