[PATCH 0/4][e2fsprogs] Enable FLEX_BG support

["Jose R. Santos" <jrs@us.ibm.com>]

The following series of patches add support creating and checking
filesystems with the FLEX_BG feature.  This feature currently groups
meta-data from a series of groups at the beginning of a flex group in
order to improve performance during heavy meta-data operations.

Changes from last time:
- When making a filesystem with FLEX_BG also enable META_BG feature.
- Allocate meta data within the META_BG group range.  
- Descriptor checking ensures bitmaps and inode tables are in the META 
  group.

Problems and TODOs:
- Fsck has some failures using FLEX_BG and resize_inode features at the
  same time.  Still investigating.
- Need to define how unallocated inode tables will look like.
- Need to create test case

-JRS