hush: fix a bug where we don't properly handle f() { a=A; b=B; }; a= f

function                                             old     new   delta
unset_local_var                                       20     274    +254
leave_var_nest_level                                   -      98     +98
set_vars_and_save_old                                128     164     +36
enter_var_nest_level                                   -      32     +32
builtin_local                                         46      50      +4
pseudo_exec_argv                                     554     544     -10
redirect_and_varexp_helper                            77      64     -13
run_pipe                                            1890    1641    -249
unset_local_var_len                                  267       -    -267
------------------------------------------------------------------------------
(add/remove: 2/1 grow/shrink: 3/3 up/down: 424/-539)         Total: -115 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

shell/hush_test/hush-vars/var_nested1.right

@@ -0,0 +1,3 @@
+Expected:AB Actual:AB
+Expected:Ab Actual:Ab
+Expected:ab Actual:ab

shell/hush_test/hush-vars/var_nested1.tests

@@ -0,0 +1,16 @@
+f() { a=A; b=B; }
+
+a=a
+b=b
+f
+echo Expected:AB Actual:$a$b
+
+a=a
+b=b
+b= f
+echo Expected:Ab Actual:$a$b
+
+a=a
+b=b
+a= b= f
+echo Expected:ab Actual:$a$b

shell/hush_test/hush-vars/var_nested2.right

@@ -0,0 +1 @@
+aB

shell/hush_test/hush-vars/var_nested2.tests

@@ -0,0 +1,2 @@
+# the bug was easier to trigger in one-liner form
+a=a; b=b; f() { a=A; b=B; }; a= f; echo $a$b