curl_multi_add_handle.3: mention the CURLMOPT_TIMERFUNCTION use
comments: remove old and wrong multi/easy interface statements
curl_multi_add_handle.3: ... that timer callback is for event-based
DISABLED: shut of test 1512 for now

It shows intermittent failures and I haven't been able to track them
down yet. Disable this test for now.
test1511: consistently terminate headers with CRLF
tests: add keywords for a couple of FTP tests
tests: add keywords for a couple of HTTP tests
tests: add 'FAILURE' keywords to tests 1409 and 1410
tests: add keywords for a couple of FILE tests
test1228: add 'HTTP proxy' to the keywords
THANKS: added contributors from the 7.32.0 release notes