Fix/csharp reserved headers and file parameter not serialising correctly #363

Job	Run time
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.7/OneOf)	2m 2s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.7/AnyOfNoCompare)	1m 17s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.7/UseDateTimeForDate)	1m 13s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.7/FormModels)	1m 16s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.8/AllOf)	1m 50s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.8/OneOf)	1m 45s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.8/Petstore)	1m 38s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.8/AnyOfNoCompare)	2m 30s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.7/Petstore)	1m 18s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.8/UseDateTimeForDate)	1m 30s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.8/FormModels)	3m 7s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.7/AnyOf)	1m 33s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.8/AnyOf)	1m 42s
Build .Net Framework projects (samples/client/petstore/csharp/generichost/net4.7/AllOf)	1m 12s
	23m 53s

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