fix issue #103 check open files limit during initialization
fix issue #103 check open files limit during initialization

Prevent database corruption due to default open file limits.
If limit is too low, print an error message and exit.

bauerj/electrum-server,spesmilo/electrum-server,Verbalist/electrum-server,dashpay/electrum-dash-server,cryptapus/electrum-server-uno,protonn/electrum-dgb-server,erasmospunk/electrum-server,spesmilo/electrum-server,fireduck64/electrum-server,cryptapus/electrum-server,eXcomm/electrum-server,cryptapus/electrum-server,lbryio/lbryum-server,GroestlCoin/electrum-grs-server,OverlordQ/electrum-server,lbryio/lbryum-server,bauerj/electrum-server,fireduck64/electrum-server,vcoin-project/electrum-server-vcn,eXcomm/electrum-server,thelazier/electrum-dash-server,dashpay/electrum-dash-server,joshafest/electrum-fnx,erasmospunk/electrum-server,thelazier/electrum-dash-server,repos-bitcoin/electrum-server,repos-bitcoin/electrum-server,joshafest/electrum-fnx,cryptapus/electrum-server-uno,shsmith/electrum-server,cryptapus/electrum-server-myr,shsmith/electrum-server,argentumproject/electrum-arg-server,pooler/electrum-ltc-server,Verbalist/electrum-server,argentumproject/electrum-arg-server,protonn/electrum-dgb-server,GroestlCoin/electrum-grs-server,cryptapus/electrum-server-myr,pooler/electrum-ltc-server,vcoin-project/electrum-server-vcn,OverlordQ/electrum-server