Merge branch 'jh/partial-clone'

The machinery to clone & fetch, which in turn involves packing and
unpacking objects, have been told how to omit certain objects using
the filtering mechanism introduced by the jh/object-filtering
topic, and also mark the resulting pack as a promisor pack to
tolerate missing objects, taking advantage of the mechanism
introduced by the jh/fsck-promisors topic.

* jh/partial-clone:
  t5616: test bulk prefetch after partial fetch
  fetch: inherit filter-spec from partial clone
  t5616: end-to-end tests for partial clone
  fetch-pack: restore save_commit_buffer after use
  unpack-trees: batch fetching of missing blobs
  clone: partial clone
  partial-clone: define partial clone settings in config
  fetch: support filters
  fetch: refactor calculation of remote list
  fetch-pack: test support excluding large blobs
  fetch-pack: add --no-filter
  fetch-pack, index-pack, transport: partial clone
  upload-pack: add object filtering for partial clone

environment.c

@@ -28,6 +28,7 @@ int warn_on_object_refname_ambiguity = 1;
 int ref_paranoia = -1;
 int repository_format_precious_objects;
 char *repository_format_partial_clone;
+const char *core_partial_clone_filter_default;
 const char *git_commit_encoding;
 const char *git_log_output_encoding;
 const char *apply_default_whitespace;