ash: more general format ${var:EXPR:EXPR}

function                                             old     new   delta
subevalvar                                          1171    1202     +31
localcmd                                             364     366      +2

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/ash_test/ash-vars/var_bash1b.right b/shell/ash_test/ash-vars/var_bash1b.right
new file mode 100644
index 0000000..fafc0f0
--- /dev/null
+++ b/shell/ash_test/ash-vars/var_bash1b.right
@@ -0,0 +1,23 @@
+all    |0123456
+4:     |456
+4:2    |45
+4:-1   |45
+4:-2   |4
+4:-3   |
+-4:    |3456
+-4:2   |34
+-4:-1  |345
+-4:-2  |34
+-4:-3  |3
+-4:-4  |
+-4:i=2 |34
+-4:i=-2|34
+-4:i=-3|3
+-4:i=-4|
+-5:    |23456
+-6:    |123456
+-7:    |0123456
+-8:    |
+-9:    |
+-9:-99 |
+Ok:0