add tests for multiple seeks
add tests for multiple seeks

ralphtheninja/leveldown,Level/leveldown,MathieuCassagne/leveldown,MathieuCassagne/leveldown,ralphtheninja/leveldown,MathieuCassagne/leveldown,ralphtheninja/leveldown,ralphtheninja/leveldown,MathieuCassagne/leveldown,Level/rocksdb,Level/rocksdb,ralphtheninja/leveldown,Level/leveldown,MathieuCassagne/leveldown,Level/rocksdb,Level/leveldown