Merge tag 'upstream/0.20.0'

Merge tag 'upstream/0.20.0'

* tag 'upstream/0.20.0': (664 commits)
  libgit2 0.20.0 "anmeldung"
  Formatting fix for cred_acquire_cb
  util: NetBSD doesn't have qsort_r either
  tests: Drop unrelated comment
  index: Free the index on git_index_open() failure
  tree-cache: Fix error message typo
  tree-cache: Don't segfault upon corruption
  tree-cache: Zero out the allocated tree children array
  tree-cache: Free the tree upon the detection of a corrupted child
  cleaning code, removing unused variables
  Add content offset to git_diff_line
  netops: fix leak
  Fix warnings
  Introduce git_cred_default for NTLM/SPNEGO auth
  Propagate auth error codes as GIT_EUSER in winhttp
  Add missing mappings to .mailmap file
  Update files that reference tests-clar
  Rename tests-clar to tests
  Fix warnings
  tests: make a few globals statics
  ...