doc: document EREs like a{,10}

Problem reported by Eric Blake in
<http://lists.gnu.org/archive/html/bug-grep/2013-04/msg00005.html>.
* NEWS: Document the bug fix.
* doc/grep.in.1: Restore documentation for this feature, but mention
that it is a GNU extension.
* doc/grep.texi (Fundamental Structure): Mention that this feature
is a GNU extension.

1 files changed, 2 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 163ee3e0..5dc0a8c2 100644
--- a/NEWS
+++ b/NEWS
@@ -79,6 +79,8 @@ GNU grep NEWS                                    -*- outline -*-
   grep -E 'a{1000000000}' now reports an overflow error rather than
   silently acting like grep -E 'a\{1000000000}'.
 
+  grep -E 'a{,10}' was not treated equivalently to grep -E 'a{0,10}'.
+
 ** New features
 
   The -R option now has a long-option alias --dereference-recursive.