implement support for commit coloring in got-read-pack for speed ok op, tracey

build with -Wmissing-prototypes ok stsp@

fix unexpected imsg error after incomplete enumeration in got-read-pack reported by jrick and op@ ok op@

memset all stack-allocated structs used to send messages; ok stsp@

zero the whole struct got_imsg_object before sending it otherwise some fields may be unitialized and fail the validation done on the receiving side. ok stsp@

fix a harmless off-by-one from previous commit

fix a bug in got_privsep_send_object_idlist() exposed by recent changes The old code did not work correctly if only a single object Id was to be sent to got-read-pack. Make got-read-pack error out if the list of commits for object enumeration is empty to catch this problem if it occurs again. Found by the send_basic test, which was failing with GOT_TEST_PACK=1 ok tracey

let got-read-pack be explicit about whether it could enumerate all objects This allows the main process to avoid looping over all object IDs again in case the pack file used for enumeration is complete. ok op@

remove trailing whitespaces

compute object size, not pointer size in this case they're luckily the same; got_imsg_object_idlist and got_imsg_reused_delta only have one size_t long field. ok stsp@

strictier validation for data received from libexec helpers use correct error code and ok stsp@

drop unused variable

use strndup instead of malloc+memcpy Simplifies the reading of the author/committer string and makes also the code shorter. ok stsp@

don't check datalen when calling recv_imsg_error recv_imsg_error already checks the size of the message, and it does so more precisely than the removed code. ok stsp@

Bring back object enumeration inside got-read-pack as a fast path. The problem that was found in the earlier version has been fixed. ok op@