Improved http_build_query (fixes reCAPTCHA)

As of PHP 5.3, the default seperator of http_build_query is
arg_separator.input, which is in some cases "&amp". This may cause some
unexpected problems i.e. reCAPTCHA doesn't work as intended.
Merge pull request #1398 from SoftCreatR/HTTPRequestFix

Improve http_build_query (fixes reCAPTCHA)
Fixed import issues
Merge branch 'master' of github.com:WoltLab/WCF
Small optimization