Rename patches applied upstream

  * patches/hurd-i386/tg-socket_flags.diff: Rename to git-socket_flags.diff.
  * patches/hurd-i386/tg-socketpair_flags.diff: Rename to
    git-socketpair_flags.diff.
  * patches/hurd-i386/tg-pipe2.diff: Rename to git-pipe2.diff.
  * patches/hurd-i386/tg-posix_thread.diff: Rename to git-posix_thread.diff.
  * patches/hurd-i386/tg-pthread_deps.diff: Rename to git-pthread_deps.diff.