perf ui browser: Add routines to compactly specify exit keys

This makes the usual idiom for specifying a series of key codes to exit
ui_browser__run() for specialized processing (search, annotate, etc) or
plain exiting the browser more compact.

It also abstracts away some more libnewt operations. At some point we'll
also replace NEWT_KEY_foo with something that can be mapped to NEWT or,
say, gtk.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <new-submission>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>