MFC r345839, r345894, r345897, r345900-r345901, r345976, r346220, r348602, r348767, r348967,
r349047-r349048, r351204-r351205, r351502, r351623, r352364, r356249-r356250, r356313,
r356434, r356628-r356629, r356636, r356657, r357421, r357716, r360359, r360428:

r345839: Assert that q can't be NULL. 'empty' is always non-NULL when DIREMPTY
r345894: Restore the ability of checking and fixing next free
r345897: Restore lfcl when LOSTDIR's chain was corrupted and overwritten
r345900: Implement checking of .' and ..' entries of subdirectory.
r345901: Fix build.
r345976: Write string constant differently to improve readability.
r346220: Don't cast result from malloc().
r348602: Don't increment cl after increment.
r348767: preen should work independently with alwaysyes and alwaysno.
r348967: Avoid out of boundary access when checking invalid long filenames.
r349047: Blankspace. No actual code change.
r349048: In ask(): override default option if any of alwaysyes/alwaysno/rdonly is
r351204: Remove redundant check and wrong fix: fat.c checks already take care
r351205: Use calloc().
r351502: Comment boot block checks and perform additional sanity checks:
r351623: Remove unneeded blank line. No functional change.
r352364: Avoid mixing cluster numbers and sector numbers. Makes code more readable.
r356249: Reduce memory footprint of fsck_msdosfs.
r356250: Revert r356249 for now as it broke GCC builds.
r356313: Reduce memory footprint of fsck_msdosfs.
r356434: fsck_msdosfs.8: document -M.
r356628: Require FAT to occupy at least one sector.
r356629: Apply typo fix from NetBSD, we have already applied all NetBSD changes so
r356636: Correct off-by-two issue when determining FAT type.
r356657: Tighten FAT checks and fix off-by-one error in corner case.
r357421: Diff reduction against NetBSD, no functional change.
r357716: Use humanize_number to format available and bad space sizes.
r360359: Fix a bug with dirty file system handling.
r360428: Do not overflow when calculating file system size.