Remove empty Thread destructor
Inherit ThreadQueueData from Mutex to avoid duplicating code
Add formatting to InspIRCd::TimeString; switch all code to use it.

m_httpd also now uses the correct timestamp format.

Windows-specific fixes by @attilamolnar, original PR #849
Add parameter to InspIRCd::TimeString for UTC time formats.

Missing doc added by @attilamolnar
Ignore safe compiler warnings in a more reliable way.