send application/json content-type for JSON response

[freddyb]

Multiple files in the web directory contain the line inevow.IRequest(ctx).setHeader("content-type", "text/plain") for JSON responses. The correct type would be application/json.

I guess this is a minor issue, though content-type confusions have caused XSS for users of Internet Explorer (though mostly when it incorrectly guesses an HTML type, I don't know if this applies with text/plain already given)

[daira]

text/plain is more likely to trigger MIME type guessing than application/$FOO (unless $FOO = octet-string), because of the prevalence of servers that use text/plain as a default when they don't know. However, Internet Explorer is generally guessing-happy unless you specifically use headers to ask it not to be.