cmd: Constify WCMD_pushd parameter.

programs/cmd/builtins.c

@@ -1418,7 +1418,8 @@ void WCMD_goto (CMD_LIST **cmdList) {
  *	Push a directory onto the stack
  */
 
-void WCMD_pushd (WCHAR *command) {
+void WCMD_pushd (const WCHAR *command)
+{
     struct env_stack *curdir;
     WCHAR *thisdir;
     static const WCHAR parmD[] = {'/','D','\0'};

programs/cmd/wcmd.h

@@ -79,7 +79,7 @@ void WCMD_output_asis_stderr (const WCHAR *message);
 void WCMD_pause (void);
 void WCMD_popd (void);
 void WCMD_print_error (void);
-void WCMD_pushd (WCHAR *);
+void WCMD_pushd (const WCHAR *command);
 void WCMD_remove_dir (WCHAR *command);
 void WCMD_rename (void);
 void WCMD_run_program (WCHAR *command, int called);