Merge branch 'maint'

* maint:
  Fix possible coredump with fast-import --import-marks
  Refactor fast-import branch creation from existing commit
  fast-import: Fix crash when referencing already existing objects
  fast-import: Fix uninitialized variable
  Documentation: fix git-config.xml generation

diff --cc Documentation/config.txt
Simple merge

diff --cc fast-import.c
Simple merge