e2freefrag: use 64-bit rbtree bitmaps

e2freefrag: use 64-bit rbtree bitmaps

Enable the use of 64-bit bitmaps, so e2freefrag will work on file
systems with the 64-bit feature enabled.  In addition, enable the
rbtree-based bitmaps, which significantly saves the amount of memory
required (from 97 megs to 1.7 megs for an empty 3T file system) at the
cost of additional CPU overhead (but we will claw back some of the
additional CPU overhead in the next commit).

Addresses-Google-Bug: 7269948

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>