SEOUL, Jan 9 (Reuters) - South Korea said on Friday it will open up its currency market to allow 24-hour trading starting in July, further removing restrictions on onshore trading in a bid to win an upgrade to developed-market status, the finance ​ministry said. After experiencing capital flight during the Asian Financial Crisis in the late 1990s, South Korea has maintained a restricted currency-trading regime, ‌which Morgan Stanley Capital International (MSCI) has called an impediment in securing a long- ...