[CRIU] Weekend update

[Pavel Emelyanov]

Hi, guys!

I've pushed some code to the repo this weekend w/o review, sorry.
It includes cleanups, bugfixes and changes the layout of how open files
are now stored in the image.

Here are the changes in the reverse order:

      check: Fix peek_off getting
      restorer: Fix ret usage in prctl macro
      rst: Open exe link fd early
      show: Print fdinfo types as names, not numbers
      show: Dont't print path len
      zdtm: Extend file_shared test
      file-ids: Fix subnode linkage
      file-ids: Show collected subtree at the end of dump
      file-ids: Fix collect genid type
      dump: Remove 2nd mappings free call
      restore: Restore cwd with fchdir
      file-ids: Enlighten ID generation and storage
      files: Sanitize fd logging
      fdinfo: Sanitize types in fdinfo_entry
      files: Split fdinfo in two parts
      file-ids: Report whether a new id was generated
      util: Fix open_image_ro definition
      image: New image file for regfiles
      files: Split regfiles info into separate file
      files: Move reg-file dumping routine into separate fn
      repo: Add mailmap file

Thanks,
Pavel