Git: Increase limit in LogChangeDialog to 1000 entries

Task-number: QTCREATORBUG-11200
Change-Id: Iff6073c4f84926a18006c1f47b30a0525134c2ba
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>