Merge branch 'bc/clone-with-git-default-hash-fix'

"git clone" that clones from SHA-1 repository, while GIT_DEFAULT_HASH set to use SHA-256 already, resulted in an unusable repository that half-claims to be SHA-256 repository with SHA-1 objects and refs. This has been corrected. * bc/clone-with-git-default-hash-fix: builtin/clone: avoid failure with GIT_DEFAULT_HASH