Mostly complete disklog2 proofs
Mostly complete disklog2 proofs

trunc_ok and extend_ok mostly went through.

read_ok now becomes tricky due to 0-padding.  We cannot simply
return the combined descriptor and data list.  But have to
filter non-zero items in the descriptor to align them.
Wrote some tedious lemma to show the equivalence of padded and
non-padded log contents.

mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl,mit-pdos/fscq-impl