hacks to get got-read-pack working on sha256 repositories

fix objectformat=sha256; handle it for real!

rename sha1.c to hash.c

include sha2.h where sha1.h was included

sed -i s/sha1/hash not exactly, some "hash" were changed back to "sha1" for the time being.

gotd, gotadmin: install packfiles and index files as 0444 gotd used 0600 (due to mkstemps(3)), gotadmin 0644; change it to 0444 since packfiles shouldn't change once created. Mirrors what git does. ok stsp@

use mkstemps(3) instead of mkstemp(3) for opening named temporary files Allows 'got commit' to use a ".diff" suffix for temporary diff files. ok op@

let callers of got_pack_create() configure rate-limiting of progress reporting Needed by future gotd(8), where progress reports will be sent to a network socket, rather than a local terminal.

move got_opentempfd() call out of got_pack_create() Future gotd(8) needs to run got_pack_create() in a chroot environment, so we can no longer open new temporary files inside got_pack_create(). ok op@

make got_pack_create() write to a file descriptor instead of a stdio FILE The old code required a seekable output file. This conflicts with requirements of future gotd(8), which will write pack file data to network sockets. ok op@

remove trailing whitespace; patch by Josiah Frentsos

If the first readdir() returns NULL err is uninitialized. This can't happen in practice, but llvm's scan-build doesn't know this. OK stsp

inline struct got_object_id in struct got_object_qid Saves us from doing a malloc/free call for every item on the list. ok op@

sort references by date for packing; newer commits should be processed first

factorize imsg_clear calls after imsg_flush failures imsg_clear frees and closes resources allocated as part of enqueueing imsgs so it's a no-op after reads. discussed with and ok stsp@