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>
diff --git a/lib/commit.tcl b/lib/commit.tcl
index b2d2d53..1c0586c 100644
--- a/lib/commit.tcl
+++ b/lib/commit.tcl
@@ -303,7 +303,7 @@
 		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.