Change regex used to check for email address validity.

Picked from http://stackoverflow.com/a/1149894/2426994
Add a test case that fails with the old regex.

Old regex:
[A-Z0-9a-z][A-Z0-9a-z._%+-]*@[A-Za-z0-9][A-Za-z0-9.-]*\\.[A-Za-z]{2,6}
Merge pull request #71 from talk-to/use-stricter-regex-in-tdt_isEmail

Merged #71 Change regex used to check email address validity.