[CRIU] images rework

[Pavel Emelyanov]

Hi.

Recent changes in CRIU change images significantly.
Summary:

0. Per-VMA file IDs are saved in shmemid field of vma image, not in fdinfo file.

1. cwd is store in separate fs-%d.img file, not fdinfo.img one. root is put
   there as well, but not yet restore. Required to make support of CLONE_FS
   and CLONE_FILES

2. All per-mm bits (code start, end, brk, etc.) are moved from core-%d.img to
   mm-%d.img file.

3. The exe file id is moved from fdinfo-%d.img to mm-%d.img. With #2 is required
   to make support for CLONE_VM.

0, 1, 2 and 3 get rid of special fdinfo-s.

Thanks,
Pavel