thanks for all the help massaging this diff

Avoids clobbering open files for delta base/accumulation, leaking file descriptors, and triggering errors from close(2) during got_repo_close() as we try to close the same file descriptor more than once.

found by tracey

This prepares for callers of got_repo_open() that cannot afford to open files in /tmp, such as gotwebd. In a follow-up change, we could ask such callers to pass in the required amount of open temporary files. One consequence is that got_repo_open() now requires the "cpath" pledge promise. Add the "cpath" promise to affected callers and remove it once the repository has been opened. ok tracey

Saves us from doing a malloc/free call for every item on the list. ok op@

otherwise we call got_repo_close with repo being NULL and segfault there. ok stsp

Avoids overhead due to readdir calls while searching a pack index. ok op@

suggested by + ok naddy

Move the detection of UUID header files to be included portably. This will have no functional effect until MacOS detection is put in place.

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@

As done elsewhere, d->namlen is not a portable field from readdir, therefore simualte this via the strlen of the directory name instead.

tested by thomas, naddy, and myself

suggested by millert ok thomas_adam

suggested by millert ok thomas_adam

sys/{tree,queue}.h are looked up via configure, and therefore are included via that mechanism.

Update portable to support changes for bloom, etc.