more platforms support egrep than grep -E, so use that instead

This commit was SVN r11797.

autogen.sh

@@ -637,7 +637,7 @@ EOF
 
         elif test -f .ompi_ignore && \
              test -s .ompi_unignore && \
-             test -z "`grep -E $USER\$\|$USER@$HOST .ompi_unignore`" ; then
+             test -z "`egrep $USER\$\|$USER@$HOST .ompi_unignore`" ; then
 
             # If we have a non-empty .ompi_unignore and our username
             # is in there somewhere, we ignore the .ompi_ignore (and