mruby/mruby — pull request #604 by skandhas (2012-12-09 13:29:38+00:00)
Title: fix incorrect checkups in check_iv_name

The checkups in check_iv_name should be more strict.

Example:
```ruby
class Test4CheckIVName
@iv = 1
@@cv = 2
end

p Test4CheckIVName.instance_variable_get(:@iv)
p Test4CheckIVName.instance_variable_get(:@@cv) # should be throw a error，beacase @@cv is a class variable, not a instance variable.
```

Ruby 1.9.x output:
```ruby
1
`@@cv' is not allowed as an instance variable name (NameError)
```

But in mruby:
```ruby
1
2
```