hush: move shell_ver from globals to main's stack.

hush: move shell_ver from globals to main's stack.

function                                             old     new   delta
hush_main                                            995    1011     +16
pseudo_exec_argv                                     253     251      -2
execvp_or_die                                         50      48      -2
maybe_set_to_sigexit                                  50      47      -3
hush_exit                                             78      75      -3
builtin_wait                                         274     271      -3
check_and_run_traps                                  205     200      -5
init_sigmasks                                        214     190     -24
builtin_trap                                         465     441     -24
reset_traps_to_defaults                              238     211     -27
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 1/9 up/down: 16/-93)            Total: -77 bytes

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>