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/adb_client.c b/adb_client.c
index 5868744..243f0fa 100644
--- a/adb_client.c
+++ b/adb_client.c
@@ -213,7 +213,7 @@
             fprintf(stdout,"* daemon started successfully *\n");
         }
         /* give the server some time to start properly and detect devices */
-        adb_sleep_ms(2000);
+        adb_sleep_ms(3000);
         // fall through to _adb_connect
     } else {
         // if server was running, check its version to make sure it is not out of date