This is mostly to fix bug:
#1759705 Cannot compare files on encrypted file system
where the problem is Windows doesn't allow copying files from encrypted file system to non-encrypted temp folder. This patch allows setting WinMerge's temp folder to encrypted file system.
There might be other use cases which can use this setting, but above bug is the most important.
This patch adds new options to select if we use system's temp folder or custom temp folder (bool) and custom temp folder's path (string). New options are set from System options in options dialog.