Create pdo_1391_string_truncation_after_short_string.phpt

[talkinnl]

Regresssion tests: Use the same Statement to insert a row with short strings first, and longer strings second.

• Issue also happens with VARCHAR( >=4002 ). Not just Max or NVARCHAR
• Issues 1391, 1393 (and possibly 1371 ?) might all have the same root cause.