hush: make ${#var} unicode-aware

This mimics bash

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

shell/hush_test/hush-misc/unicode1.tests

@@ -0,0 +1,13 @@
+LANG=en_US.UTF-8
+
+# A combining character U+300
+a=`printf "\xcc\x80"`
+# Should print 1
+echo ${#a}
+
+# A Japanese katakana charachter U+30a3
+a=`printf "\xe3\x82\xa3"`
+# Should print 1
+echo ${#a}
+
+echo Ok