bump, go back to git version numbers after 0.3.0 release
minor, clearly indicate why rename() fails in cmd_build()
minor, don't allow index file names of length 0
minor, split index file name into dirname and basename ...

and in cmd_build() chdir() to target dir first, so the temp file
resides right next to the final target file.
Merge branch 'tool/gandaux'

* tool/gandaux:
  minor, split index file name into dirname and basename ...
  minor, don't allow index file names of length 0
  minor, clearly indicate why rename() fails in cmd_build()