Add support for union without brackets and with limit

[tomershay]

The parser misplaces the LIMIT clause when parsing a UNION query that doesn't include brackets.

The original query:
select col from tbl union distinct select col2 from tbl order by test limit 100;
The query after parsing (before the fix):
SELECT tbl.col FROM tbl UNION DISTINCT SELECT tbl.col2 FROM tbl LIMIT 100 ORDER BY test

Note that the LIMIT clause shows up before the ORDER BY clause, which is invalid.

After the fix, the query parses as the same as the original query.

Fixes #1018
Fixes #1116

[coveralls]

Coverage remained the same at 88.481% when pulling e86b7ad on tomershay:support_union_without_bracks_and_with_limit into bcc683a on JSQLParser:master.