Merge branch 'db/vcs-helper'

Merge branch 'db/vcs-helper'

* db/vcs-helper:
  Makefile: remove remnant of separate http/https/ftp helpers
  Use a clearer style to issue commands to remote helpers
  Make the "traditionally-supported" URLs a special case
  Makefile: install hardlinks for git-remote-<scheme> supported by libcurl if possible
  Makefile: do not link three copies of git-remote-* programs
  Makefile: git-http-fetch does not need expat
  http-fetch: Fix Makefile dependancies
  Add transport native helper executables to .gitignore
  git-http-fetch: not a builtin
  Use an external program to implement fetching with curl
  Add support for external programs for handling native fetches