Preparation work for adb to support USB vendor Ids provided by SDK add-ons.

Added usb_vendors.* which handles creating (and deleting) a list of vendor ids.
This list is meant to be used everywhere the built-in lists (usb_osx), or the
built-in vendor IDs (transport_usb)  were used.

For now the list is only built with the built-in VENDOR_ID_*. Next step
is to read a small file created from all the SDK add-on.

Other misc changes: made is_adb_interface present only if ADB_HOST is true
to prevent accessing a list that doesn't exist (usb_vendors is only
compiled for the host version of adb).
diff --git a/usb_vendors.c b/usb_vendors.c
new file mode 100644
index 0000000..f949249
--- /dev/null
+++ b/usb_vendors.c
@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2009 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "usb_vendors.h"
+
+#include "sysdeps.h"
+#include <stdio.h>
+#include "adb.h"
+
+int* vendorIds = NULL;
+unsigned vendorIdCount = 0;
+
+void usb_vendors_init(void) {
+    /* for now, only put the built-in VENDOR_ID_* */
+    vendorIdCount = 2;
+    vendorIds = (int*)malloc(vendorIdCount * sizeof(int));
+    vendorIds[0] = VENDOR_ID_GOOGLE;
+    vendorIds[1] = VENDOR_ID_HTC;
+}
+
+void usb_vendors_cleanup(void) {
+    if (vendorIds != NULL) {
+        free(vendorIds);
+        vendorIds = NULL;
+        vendorIdCount = 0;
+    }
+}