Add dedicated thread for writing errors into disk.
Add dedicated thread for writing errors into disk.

simonzhangsm/voltdb,VoltDB/voltdb,wolffcm/voltdb,kumarrus/voltdb,wolffcm/voltdb,zuowang/voltdb,paulmartel/voltdb,kumarrus/voltdb,ingted/voltdb,zuowang/voltdb,wolffcm/voltdb,paulmartel/voltdb,deerwalk/voltdb,paulmartel/voltdb,deerwalk/voltdb,ingted/voltdb,VoltDB/voltdb,deerwalk/voltdb,VoltDB/voltdb,wolffcm/voltdb,simonzhangsm/voltdb,kumarrus/voltdb,VoltDB/voltdb,paulmartel/voltdb,migue/voltdb,VoltDB/voltdb,migue/voltdb,creative-quant/voltdb,zuowang/voltdb,kumarrus/voltdb,zuowang/voltdb,ingted/voltdb,ingted/voltdb,wolffcm/voltdb,kumarrus/voltdb,kumarrus/voltdb,wolffcm/voltdb,flybird119/voltdb,migue/voltdb,paulmartel/voltdb,creative-quant/voltdb,simonzhangsm/voltdb,zuowang/voltdb,flybird119/voltdb,migue/voltdb,simonzhangsm/voltdb,creative-quant/voltdb,flybird119/voltdb,zuowang/voltdb,flybird119/voltdb,creative-quant/voltdb,flybird119/voltdb,simonzhangsm/voltdb,zuowang/voltdb,wolffcm/voltdb,paulmartel/voltdb,deerwalk/voltdb,deerwalk/voltdb,ingted/voltdb,zuowang/voltdb,flybird119/voltdb,simonzhangsm/voltdb,paulmartel/voltdb,migue/voltdb,flybird119/voltdb,ingted/voltdb,migue/voltdb,deerwalk/voltdb,flybird119/voltdb,ingted/voltdb,simonzhangsm/voltdb,VoltDB/voltdb,creative-quant/voltdb,creative-quant/voltdb,simonzhangsm/voltdb,creative-quant/voltdb,VoltDB/voltdb,creative-quant/voltdb,migue/voltdb,ingted/voltdb,wolffcm/voltdb,deerwalk/voltdb,paulmartel/voltdb,kumarrus/voltdb,kumarrus/voltdb,deerwalk/voltdb,migue/voltdb