Prepend mpirun to mrgddb, mrgscr and mrgddb to avoid problems with parallel builds.
 Add list of required_files to the Nodes of the Flow
 Fix typos
 Use new variable gw_kbpolicy for GW calculations (default is 1)
Merge remote-tracking branch 'mpmaster/master'
 Use gw_kbpolicy=1 for GW calculations.
Merge remote-tracking branch 'mpmaster/master'
 Rename gw_kbpolicy to gw_qprange
Merge remote-tracking branch 'mpmaster/master'
 Code cleanup
 Try mrgddb with and without mpirun
  Popen import was erroneously removed in the last commit
 Fix typo
Merge remote-tracking branch 'mpmaster/master'
 Prefer LibYaml to pure python version
 Don't call straceback is yaml.load raises an exeptions
 Use which("sendmail") to get the abspath of the executable
 Extract autoparal section from the main output file
Getting specie symbol simplified
Add a nionic_step to Vasprun which always has the total number of ionic steps,
regardless of ionic_step_skip.