grep: fix --devices=ACTION (-D) so stdin is once again exempt

An oversight in the 2.11 changes made it so "echo x|grep x" would
fail for those who set GREP_OPTIONS=--devices=skip.

* src/main.c (grepdesc): Ignore skip-related options when reading
from standard input.
* tests/skip-device: New file.  Test for the above.
* tests/Makefile.am (TESTS): Add it.
* doc/grep.texi (File and Directory Selection): Clarify this point,
documenting the stdin exemption.
* NEWS (Bug fixes): Mention it, and add a few "[fixed in ...] notes.
Reported by Tino Keitel in http://bugs.debian.org/669084,
and forwarded to bug-grep by Aníbal Monsalve Salazar.

1 files changed, 5 insertions, 4 deletions

diff --git a/src/main.c b/src/main.c
index 82cae33c..c5a84898 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1367,10 +1367,11 @@ grepdesc (int desc, int command_line)
         suppressible_error (filename, errno);
       return status;
     }
-  if ((directories == SKIP_DIRECTORIES && S_ISDIR (st.st_mode))
-      || ((devices == SKIP_DEVICES
-           || (devices == READ_COMMAND_LINE_DEVICES && !command_line))
-          && is_device_mode (st.st_mode)))
+  if (desc != STDIN_FILENO
+      && ((directories == SKIP_DIRECTORIES && S_ISDIR (st.st_mode))
+          || ((devices == SKIP_DEVICES
+               || (devices == READ_COMMAND_LINE_DEVICES && !command_line))
+              && is_device_mode (st.st_mode))))
     goto closeout;
 
   /* If there is a regular file on stdout and the current file refers