Thin-Client User Configuration
Changes are needed to support using the standard global git config file for thin-client users.
Following changes to refactor the config backend (!153 (merged)), attempts to open a repository while running in thin-client mode are now blocked as there's no guarantee the current windows user for the application server is the same as the user connecting via thin-client.
In order to support multiple users connecting via thin-client, changes are needed to locate/copy the global git config file for the current user to a temporary location on the application server and opening it in a read-only manner (any changes to the original would require a restart before taking effect).
Changes would be required wherever git_config_open_default is currently used (to initialize both the system/user config backends).