git-gui: Add menu option to include only selected files.

When the user selects a number of files they would typically expect
to be able to act on that selection, such as by including those files
into the next commit.

So we now have a menu option under the Commit menu that lets the user
include only the selection, rather than everything.  If there is no
selection but there is a file in the diff viewer than we consider that
to be the selection (a selection of 1).  Unfortunately we don't disable
this option yet when there's nothing selected to include, but this is
probably not a big deal as there are very few situations where there
are no selected files.
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>

git-gui

@@ -1853,14 +1853,14 @@ proc do_rescan {} {
 	rescan {set ui_status_value {Ready.}}
 }
 
-proc do_include_all {} {
+proc include_helper {txt paths} {
 	global file_states current_diff
 
 	if {![lock_index begin-update]} return
 
 	set pathList [list]
 	set after {}
-	foreach path [array names file_states] {
+	foreach path $paths {
 		switch -- [lindex $file_states($path) 0] {
 		AM -
 		MM -
@@ -1877,12 +1877,33 @@ proc do_include_all {} {
 		unlock_index
 	} else {
 		update_index \
-			"Including all modified files" \
+			$txt \
 			$pathList \
 			[concat $after {set ui_status_value {Ready to commit.}}]
 	}
 }
 
+proc do_include_selection {} {
+	global current_diff selected_paths
+
+	if {[array size selected_paths] > 0} {
+		include_helper \
+			{Including selected files} \
+			[array names selected_paths]
+	} elseif {$current_diff ne {}} {
+		include_helper \
+			"Including [short_path $current_diff]" \
+			[list $current_diff]
+	}
+}
+
+proc do_include_all {} {
+	global file_states
+	include_helper \
+		{Including all modified files} \
+		[array names file_states]
+}
+
 set GIT_COMMITTER_IDENT {}
 
 proc do_signoff {} {
@@ -2442,6 +2463,11 @@ lappend disable_on_lock \
 	-font font_ui
 lappend disable_on_lock \
 	[list .mbar.commit entryconf [.mbar.commit index last] -state]
+.mbar.commit add command -label {Include Selected Files} \
+	-command do_include_selection \
+	-font font_ui
+lappend disable_on_lock \
+	[list .mbar.commit entryconf [.mbar.commit index last] -state]
 .mbar.commit add command -label {Include All Files} \
 	-command do_include_all \
 	-accelerator $M1T-I \