Expression parser does not tried "foo" 10 as a valid amount

[jwiegley]

From @oaf-edwin: Something like "ab cd" 17 is also a valid amount. But it can't even be parsed properly in an expression. This time it's because expr_t::token_t::next() gives precedence to quoted string before literal amount (token.cc line 219 versus the lines 380ff). Perhaps when it finds a quoted string it ought to look ahead to see if a number follows.