1. Added docstring at head of the file to start inline documentation. 2. Minor change in Xia2run.__populate() to try and make log file    assignment a little more efficient.
1. Added docstring at head of the file to start inline documentation.
2. Minor change in Xia2run.__populate() to try and make log file
   assignment a little more efficient.

xia2/xia2,xia2/xia2