Fixes for 5.5:

- Minor documentation fixes
- Fix a file corruption due to read racing with an insert range
operation.
- Fix log reservation overflows when allocating large rt extents
- Fix a buffer log item flags check
- Don't allow administrators to mount with sunit= options that will
cause later xfs_repair complaints about the root directory being
suspicious because the fs geometry appeared inconsistent
- Fix a non-static helper that should have been static
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