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.h b/usb_vendors.h
new file mode 100644
index 0000000..43e5f99
--- /dev/null
+++ b/usb_vendors.h
@@ -0,0 +1,26 @@
+/*
+ * 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.
+ */
+
+#ifndef __USB_VENDORS_H
+#define __USB_VENDORS_H
+
+extern int* vendorIds;
+extern unsigned  vendorIdCount;
+
+void usb_vendors_init(void);
+void usb_vendors_cleanup(void);
+
+#endif
\ No newline at end of file