perf tools: Complete tracepoint event names

Currently tracepoint events cannot be completed because they contain a
colon (:) character.  The colon is considered as a word separator when
bash completion is done - variable COMP_WORDBREAKS contains colon - so
if a word being completed contains a colon it can be a problem.

Recent versions of bash completion provide -n switch to
_get_comp_words_by_ref and __ltrim_colon_completions functions in
order to resolve this issue.  Copy the latter in case not exists.

Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: David Ahern <dsahern@gmail.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>