Correctly parse RegExp literals in places where they should be allowed.

[dbatyai]

Currently we fail to parse RegExp literals in some places, where they should be allowed.
For example

if (true) /abc/.exec("abc");

if (true) {} /abc/.exec("abc");

var a
/abc/.exec("abc");

should all be valid.

[wateret]

Closing as #660 landed.