all/windows: Be case in-sensitive about pattern matching. (#3682)

Resource strings and paths are case insensitive on windows
deployments but if user happens to use upper case instead of
lower case for certain configuration params like bucket
policies and bucket notification config. We might not honor
them which leads to a wrong behavior on windows.

This is windows only behavior, for all other platforms case
is still kept sensitive.

cmd/tree-walk_test.go

@@ -135,7 +135,7 @@ func testTreeWalkPrefix(t *testing.T, listDir listDirFunc, isLeaf isLeafFunc) {
 
 	// Check if all entries received on the channel match the prefix.
 	for res := range twResultCh {
-		if !strings.HasPrefix(res.entry, prefix) {
+		if !hasPrefix(res.entry, prefix) {
 			t.Errorf("Entry %s doesn't match prefix %s", res.entry, prefix)
 		}
 	}