git-gui: deal with unknown files when pressing the "Stage Changed" button

As a shortcut the "Stage Changed" button can be used to stage all current
changes in the worktree which are not set to ignore. Previously unknown
files would be ignored. The user might want to say: "Just save everything
in my worktree". To support this workflow we now ask whether the user also
wants to stage the unknown files if there are some present.

Signed-off-by: Heiko Voigt <hvoigt@hvoigt.net>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>

lib/index.tcl

@@ -356,12 +356,21 @@ proc do_add_all {} {
 	global file_states
 
 	set paths [list]
+	set unknown_paths [list]
 	foreach path [array names file_states] {
 		switch -glob -- [lindex $file_states($path) 0] {
 		U? {continue}
 		?M -
 		?T -
 		?D {lappend paths $path}
+		?O {lappend unknown_paths $path}
+		}
+	}
+	if {[llength $unknown_paths]} {
+		set reply [ask_popup [mc "There are unknown files do you also want
+to stage those?"]]
+		if {$reply} {
+			set paths [concat $paths $unknown_paths]
 		}
 	}
 	add_helper {Adding all changed files} $paths