Prevent hangs from IM requests with the main thread busy

Prevent hangs from IM requests with the main thread busy

* src/android.c (android_select): Clear `android_urgent_query'.
(android_check_query): Make static.  Clear
`android_urgent_query'.
(android_check_query_urgent): New function; work like
`android_check_query', but only answer urgent queries.
(android_answer_query, android_end_query): Clear urgent query
flag.
(android_run_in_emacs_thread): Initially wait two seconds for
the query to run from the keyboard loop; upon a timeout, set
`android_urgent_query' to true and wait for it to run while
reading async input.
* src/android.h: Update prototypes.
* src/keyboard.c (handle_async_input): Call
`android_check_query_urgent'.