TxEngine: use segment locks rather than global lock
TxEngine: use segment locks rather than global lock

jankotek/MapDB,morfeo8marc/mapdb,ffjiao/mapdb,jankotek/MapDB,sumit784/mapdb,pettermahlen/mapdb,cocosli/mapdb,olupas/MapDB,jankotek/mapdb,binarytemple/mapdb,lamfire/mapdb,hangum/mapdb,olupas/MapDB,jankotek/mapdb,mebigfatguy/mapdb,SleimanJneidi/mapdb,ringoluo/mapdb,codeaudit/mapdb,mebigfatguy/mapdb