[tramp] tramp-adb-program problem

[Neal Becker]

tramp-adb assumes adb is found in a subdir called 'platform-tools'.

Now some distributions (e.g., Fedora) ship adb and put into standard directories
(e.g., /usr/bin/adb)

Can we make tramp-adb more flexible to support this?  The current code says:

(defun tramp-adb-program ()
  "The Android Debug Bridge."
  (expand-file-name "platform-tools/adb" tramp-adb-sdk-dir))