Harshavardhana 926c75d0b5 api: Set appropriate content-type for success/error responses. (#3537)
Golang HTTP client automatically detects content-type but
for S3 clients this content-type might be incorrect or
might misbehave.

For example:

```
Content-Type: text/xml; charset=utf-8
```

Should be
```
Content-Type: application/xml
```

Allow this to be set properly.
2017-01-06 00:37:00 -08:00
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