StreamHandler: Set $useLocking to true by default

[tomsommer]

Would it not make sense to set $useLocking to true by default? Otherwise you risk random concurrency/permission errors.

monolog/src/Monolog/Handler/StreamHandler.php

Line 39 in 7405bb5

* @param Boolean $useLocking Try to lock log file before doing any writes

monolog/src/Monolog/Handler/RotatingFileHandler.php

Line 45 in 07b6c1c

* @param Boolean $useLocking Try to lock log file before doing any writes

[Seldaek]

As per #379 - this is only an issue if you log long lines or in very odd setups. For most use cases locking isn't needed even with high concurrency, so I don't think it's a good idea to enable by default.