netbsd dirent.h, import sys/sys *.h, mfs cleanup

. add all sys/sys headers not already present to help compiling
. take netbsd dirent.h and struct dirent; main result is
introducing d_type and

netbsd dirent.h, import sys/sys *.h, mfs cleanup

. add all sys/sys headers not already present to help compiling
. take netbsd dirent.h and struct dirent; main result is
introducing d_type and d_namlen that have to be set by getdents()
in all FS code implementing it
. d_off is gone
. alignment of the struct has become 8 bytes instead of 4
. remove _MAX_BLOCK_SIZE, _MIN_BLOCK_SIZE, _STATIC_BLOCK_SIZE
. libminlib: cleanup unused yet duplicate code
. mfs: throw out the long-broken v1, v2 support
. new test for dirent contents filled by getdents()

Change-Id: I1459755c7ba5e5d1c9396d3a587ce6e63ddc283e

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