hush: add support for special vars in braces

Some people like to use ${?} rather than $?, so make sure we support all
the special single char vars that use this form.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

shell/hush.c

@@ -5303,6 +5303,9 @@ static int handle_dollar(o_string *as_string,
 					all_digits = true;
 					goto char_ok;
 				}
+				/* They're being verbose and doing ${?} */
+				if (i_peek(input) == '}' && strchr("$!?#*@_", ch))
+					goto char_ok;
 			}
 
 			if (expansion < 2

shell/hush_test/hush-vars/param_expand_indicate_error.right

@@ -1,5 +1,4 @@
 hush: syntax error: unterminated ${name}
-hush: syntax error: unterminated ${name}
 0
 0
 _

shell/hush_test/hush-vars/param_expand_indicate_error.tests

@@ -1,7 +1,7 @@
 # do all of these in subshells since it's supposed to error out
 
 # first try some invalid patterns
-"$THIS_SH" -c 'echo ${?}'
+#"$THIS_SH" -c 'echo ${?}' -- this is valid as it's the same as $?
 "$THIS_SH" -c 'echo ${:?}'
 
 # then some funky ones

shell/hush_test/hush-vars/var1.right

@@ -1,4 +1,4 @@
 http://busybox.net
 http://busybox.net_abc
-1
-1
+1 1
+1 1

shell/hush_test/hush-vars/var1.tests

@@ -4,6 +4,6 @@ echo $URL
 echo ${URL}_abc
 
 true
-false; echo $?
+false; echo $? ${?}
 true
-{ false; echo $?; }
+{ false; echo $? ${?}; }

shell/hush_test/hush-vars/var3.right

@@ -1,3 +1,2 @@
 hush: syntax error: unterminated ${name}
 hush: syntax error: unterminated ${name}
-hush: syntax error: unterminated ${name}

shell/hush_test/hush-vars/var3.tests

@@ -1,4 +1,4 @@
 # reject invalid vars
 "$THIS_SH" -c 'echo ${1q}'
 "$THIS_SH" -c 'echo ${&}'
-"$THIS_SH" -c 'echo ${$}'
+#"$THIS_SH" -c 'echo ${$}' -- this is valid as it's the same as $$