Fixing Bug in JSX transformer

The bug fixed by this commit prevented the correct parsing of
`var` statements with multiple variables being declared. Instead
of trying to parse a whole 'variable declarations' (a `var`
statement with all its declarations), this visitor now only
parses single 'variable declarators'.
Removed duplicate object type check
Merge pull request #27 from seiffert/master

JSX Transformer / DisplayName Visitor: Multiple declarations with one `var` statement