By Nidal al-Mughrabi Gaza (Reuters) - Egypt opened the Rafah border crossing on Saturday to allow Palestinians to travel in and out of the Gaza Strip for the first time in three months, in a possible sign of easing tension between Cairo and Gaza's dominant Islamist Hamas movement. Gaza, a small impoverished coastal enclave, is under blockade by neighboring Israel, and Egypt has kept its Rafah crossing largely shut since Cairo's Islamist president was toppled by the army in 2013. A Palestinian official said seven trucks with building materials for the private sector entered Gaza on Saturday, the first time since 2007 that Egypt has allowed a commercial shipment via Rafah, which is mainly for passengers and humanitarian aid.