Refactor definition of special variables.

This ensures that the parser and other places that refer to special
variables can use the same list.

src/ShellCheck/Data.hs

@@ -47,6 +47,8 @@ variablesWithoutSpaces = specialVariablesWithoutSpaces ++ [
     "COLUMNS", "HISTFILESIZE", "HISTSIZE", "LINES"
   ]
 
+specialVariables = specialVariablesWithoutSpaces ++ ["@", "*"]
+
 arrayVariables = [
     "BASH_ALIASES", "BASH_ARGC", "BASH_ARGV", "BASH_CMDS", "BASH_LINENO",
     "BASH_REMATCH", "BASH_SOURCE", "BASH_VERSINFO", "COMP_WORDS", "COPROC",

src/ShellCheck/Parser.hs

@@ -69,7 +69,7 @@ variableChars = upper <|> lower <|> digit <|> oneOf "_"
 functionChars = variableChars <|> oneOf ":+?-./^@"
 -- Chars to allow in functions using the 'function' keyword
 extendedFunctionChars = functionChars <|> oneOf "[]*=!"
-specialVariable = oneOf "@*#?-$!"
+specialVariable = oneOf (concat specialVariables)
 paramSubSpecialChars = oneOf "/:+-=%"
 quotableChars = "|&;<>()\\ '\t\n\r\xA0" ++ doubleQuotableChars
 quotable = almostSpace <|> oneOf quotableChars