Cannot export Reports to CSV in Internet Explorer over https://

Sigh, I hate IE. So to summarize the Microsoft issue, IE is incapable of piping data to a helper application like Office, so it must save the data to disk first then tell Office to open that data. But IE will refuse to write it to disk if you've told it not to "cache" the data, since that would be violating the no-cache directive. That means there's no way to download dynamic data over HTTPS if you're using IE - all data has to be cache-able in order for IE to open it.

That's unacceptable for things like Ubercart file downloads, if we need to control how many times a file is downloaded. Caching reports isn't so much of a problem. I think we can fix this throughout Ubercart by removing the cache control headers and then fooling IE by appending a dynamic URL argument like "?time()" which will make each and every download link unique and therefore IE will never find the data in its cache. I'm going to have to test this on file downloads first before I add this to Ubercart - don't want to break those ...

Patch attached to fix this for CSV report downloads, and that also corrects a minor spelling mistake in the same function. The same patch file can also be applied to the 5.x branch.

Thanks. Committed.