Need wide-character version of qgetenv() (qwgetenv?)

On Windows, it's possible for environment variables to be set to UTF-16 strings; consider for instance TEMP=C:\权时. These are mangled if passed through qgetenv() and then QString::fromLocal8Bit(). (Unfortunately, I don't have any more detail than that; I personally don't have a Windows development environment.)

Per http://msdn.microsoft.com/en-us/library/tb2sfw2z.aspx, there is a wgetenv_s to go with the getenv_s} that {{qgetenv currently uses. It sounds like it's more efficient (in an application whose entry point is _wmain or equivalent, which I assume is true for Qt/Windows applications) to use _exclusively _wgetenv_s, so I'd like to suggest the following cluster of changes:

• Add qwgetenv which returns a QString. On Windows, this calls _wgetenv_s; on non-Windows, it calls getenv followed by QString::fromLocal8Bit.

• Change the existing qgetenv, qEnvironmentVariableIsSet, and qEnvironmentVariableIsEmpty so that, on Windows, they also use _wgetenv_s. qgetenv would feed the result through QString::toLocal8Bit before returning.

• As long as we're messing with this anyway, a full complement of QString/QByteArray/const char */const wchar_t * overloads for all of these functions would be nice.