nicoseiga: fix regression with http redirects.

3cdf67920 changed it so that Danbooru::Http follows redirects by
default. This broke some things in the Nico Seiga strategy, so disable
following redirects in the Nico Seiga API client for now.

Also change it so that Danbooru::Http follows redirects after a POST
request (by setting `strict: false`). Nico Seiga needs this because it
sends a redirect after we POST the login form.

app/logical/danbooru/http.rb

@@ -6,7 +6,7 @@ module Danbooru
     attr_writer :cache, :http
 
     class << self
-      delegate :get, :put, :post, :delete, :cache, :timeout, :auth, :basic_auth, :headers, to: :new
+      delegate :get, :put, :post, :delete, :cache, :follow, :timeout, :auth, :basic_auth, :headers, to: :new
     end
 
     def get(url, **options)
@@ -29,6 +29,10 @@ module Danbooru
       dup.tap { |o| o.cache = expiry.to_i }
     end
 
+    def follow(*args)
+      dup.tap { |o| o.http = o.http.follow(*args) }
+    end
+
     def timeout(*args)
       dup.tap { |o| o.http = o.http.timeout(*args) }
     end
@@ -77,7 +81,7 @@ module Danbooru
 
     def http
       @http ||= ::HTTP.
-        follow(max_hops: MAX_REDIRECTS).
+        follow(strict: false, max_hops: MAX_REDIRECTS).
         timeout(DEFAULT_TIMEOUT).
         use(:auto_inflate).
         headers(Danbooru.config.http_headers).