soup-message: minor fixups to soup_message_set_request/response_body()
soup-message: minor fixups to soup_message_set_request/response_body()

g_warn_if_fail() if the Content-Type is invalid, and impove the
annotations.

https://bugzilla.gnome.org/show_bug.cgi?id=686766

jwendell/libsoup,fanc999/libsoup,fanc999/libsoup,fanc999/libsoup,jwendell/libsoup,fanc999/libsoup,jwendell/libsoup,jwendell/libsoup,jwendell/libsoup,fanc999/libsoup