Switch grep from non-portable BRE to portable ERE

This makes the grep usage fully POSIX compliant.  The ability to
enable ERE features in BRE using backslash is a GNU extension.

Signed-off-by: Marcel Telka <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: mtelka

mergetools/vimdiff

@@ -325,7 +325,7 @@ gen_cmd () {
 		fi
 
 		# If this is a single window diff with all the buffers
-		if ! echo "$tab" | grep ",\|/" >/dev/null
+		if ! echo "$tab" | grep -E ",|/" >/dev/null
 		then
 			CMD="$CMD | silent execute 'bufdo diffthis'"
 		fi

t/t1404-update-ref-errors.sh

@@ -100,7 +100,7 @@ df_test() {
 		printf "%s\n" "delete $delname" "create $addname $D"
 	fi >commands &&
 	test_must_fail git update-ref --stdin <commands 2>output.err &&
-	grep "fatal:\( cannot lock ref $SQ$addname$SQ:\)\? $SQ$delref$SQ exists; cannot create $SQ$addref$SQ" output.err &&
+	grep -E "fatal:( cannot lock ref $SQ$addname$SQ:)? $SQ$delref$SQ exists; cannot create $SQ$addref$SQ" output.err &&
 	printf "%s\n" "$C $delref" >expected-refs &&
 	git for-each-ref --format="%(objectname) %(refname)" $prefix/r >actual-refs &&
 	test_cmp expected-refs actual-refs