bug#15255: coreutils should requires "patch" command 2.6 or later

[FUJIWARA Katsunori]

With recent coreutils, "patch" command 2.5.9 causes failure of
"./bootstrap" as below:

  gnulib/gnulib-tool: *** patch file gl/modules/tempname.diff didn't apply 
cleanly
  gnulib/gnulib-tool: *** Stop.
  missing header for unified diff at line 12 of patch
  The text leading up to this was:
  --------------------------
  |
  | Files:
  | lib/tempname.c
  --------------------------
  File to patch: EOF
  Skip this patch? [y]
  1 out of 1 hunk ignored
  gnulib/gnulib-tool: *** patch file gl/modules/tempname.diff didn't apply 
cleanly
  gnulib/gnulib-tool: *** Stop.
  ./bootstrap[348]: build-aux/prefix-gnulib-mk: not found [No such file or 
directory]
  ./bootstrap: bootstrap_post_import_hook failed

"patch" command 2.6 or later can avoid this error.

"./bootstrap" should check not only availability of "patch" command,
but also version of it.

diff --git a/bootstrap.conf b/bootstrap.conf
index 0863590..2535b20 100644
--- a/bootstrap.conf
+++ b/bootstrap.conf
@@ -324,7 +324,7 @@ git        1.4.4
 gperf      -
 gzip       -
 makeinfo   4.13
-patch      -
+patch      2.6
 perl       5.5
 rsync      -
 tar        -

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[FUJIWARA Katsunori]                             address@hidden