Merge branch 'tb/credential-long-lines'

The implementation of credential helpers used fgets() over fixed
size buffers to read protocol messages, causing the remainder of
the folded long line to trigger unexpected behaviour, which has
been corrected.

* tb/credential-long-lines:
  contrib/credential: embiggen fixed-size buffer in wincred
  contrib/credential: avoid fixed-size buffer in libsecret
  contrib/credential: .gitignore libsecret build artifacts
  contrib/credential: remove 'gnome-keyring' credential helper
  contrib/credential: avoid fixed-size buffer in osxkeychain
  t/lib-credential.sh: ensure credential helpers handle long headers
  credential.c: store "wwwauth[]" values in `credential_read()`

Author: gitster