Support for 3rd party USB Vendor IDs in adb.

Vendor IDs are read from ~/.android/adb_usb.ini. The format is very simple:
1 number per line. First number is ID count, followed by the ID themselves.
Lines starting with # are considered comments.

Other misc changes: moved VENDOR_ID_* to usb_vendors.c to prevent direct
access. Made transport_usb.c reuse the USB constant introduced in usb_osx
(moved them to adb.h)
diff --git a/usb_vendors.h b/usb_vendors.h
index 43e5f99..43790b9 100644
--- a/usb_vendors.h
+++ b/usb_vendors.h
@@ -17,10 +17,9 @@
 #ifndef __USB_VENDORS_H
 #define __USB_VENDORS_H
 
-extern int* vendorIds;
+extern int vendorIds[];
 extern unsigned  vendorIdCount;
 
 void usb_vendors_init(void);
-void usb_vendors_cleanup(void);
 
 #endif
\ No newline at end of file