git-gui: Make commit log messages end with a newline

Concatenating commit log messages from multiple commits works better
when all of the commits end with a clean line break.

Its good to be strict in what you create, and lenient in what you
accept, and since we're creating here, we should always try to
Do The Right Thing(tm).

Signed-off-by: Bernt Hansen <bernt@alumni.uwaterloo.ca>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

lib/commit.tcl

@@ -303,7 +303,7 @@ A rescan will be automatically started now.
 		puts stderr [mc "warning: Tcl does not support encoding '%s'." $enc]
 		fconfigure $msg_wt -encoding utf-8
 	}
-	puts -nonewline $msg_wt $msg
+	puts $msg_wt $msg
 	close $msg_wt
 
 	# -- Create the commit.