configure: Call the variable $NIX_STORE_PROGRAM, not $NIX_STORE.

Dependencies

• [2] XVBNSBNG configure: Make sure we get a recent `nix-store'.
• [3] FV2M6MOT hydra: use autoconf/-make
• [4] 2KJFOYGS hydra: Actually check for Nix in `configure'.

Change contents

• replacement in configure.ac at line 44
  [2.32]→[2.32:68](∅→∅)
  − NEED_PROG([NIX_STORE], [nix-store])
  [2.32]

  [2.68]
  + NEED_PROG([NIX_STORE_PROGRAM], [nix-store])
• replacement in configure.ac at line 46
  [2.69]→[2.69:174](∅→∅)
  − AC_MSG_CHECKING([whether $NIX_STORE is recent enough])

  − if "$NIX_STORE" --timeout 123 -q > /dev/null 2>&1
  [2.69]

  [2.174]
  + AC_MSG_CHECKING([whether $NIX_STORE_PROGRAM is recent enough])

  + if "$NIX_STORE_PROGRAM" --timeout 123 -q > /dev/null 2>&1
• replacement in configure.ac at line 52
  [2.233]→[2.233:323](∅→∅)
  − AC_MSG_ERROR([`$NIX_STORE' doesn't support `--timeout'; please use a newer version.])
  [2.233]

  [2.323]
  + AC_MSG_ERROR([`$NIX_STORE_PROGRAM' doesn't support `--timeout'; please use a newer version.])