The failure on Windows is a side effect of a bigger problem that exists on
all platforms. The reason it fails on Windows is because on Windows
rename("o","n") will fail if "n" exists. The deeper problem is that the
rename should not even be taking place. The second error is that if we do
an ALTER algorithm=INPLACE it will reset the discarded flag and create a
new .ibd file. In essence, allowing a NULL IMPORT. Some of the tests were
actually written that made use of this behaviour. This is wrong.
					        
The fix is to drop any temp tables and prevent rename on disk. Make the
new table inherit the discarded flag. Add a debug check in the rename
function that mimics Windows behaviour. This helped in reproducing the
underlying problem on Linux too.

rb://1389 Approved by Marko Makela