Correct comments in testdir makefiles. (John Beckett)
diff --git a/src/testdir/Make_dos.mak b/src/testdir/Make_dos.mak
index 6deca3d..00ceed2 100644
--- a/src/testdir/Make_dos.mak
+++ b/src/testdir/Make_dos.mak
@@ -1,5 +1,5 @@
 #
-# Makefile to run al tests for Vim, on Dos-like machines.
+# Makefile to run all tests for Vim, on Dos-like machines.
 #
 # Requires a set of Unix tools: echo, diff, etc.