Overly permissive parsing

[GoogleCodeExporter]

There are many syntax cornercases where the parser could report a syntax error 
but currently doesn't.

012     <- invalid leading digit(s)

12x     <- concatenated symbol

( . 12) <- empty improper list

12.     <- empty decimal places

12..    <- accepted at toplevel only. why?

#\spaceout <- valid char + trailing data 

#twice  <- boolean + trailing data

and probably more

Original issue reported on code.google.com by aohelin on 4 Jan 2012 at 7:59