CVE-2019-9740: reject control characters in HTTP URL paths in
httplib.HTTPConnection.putrequest to prevent CRLF header injection
CVE-2019-18348: reject control characters in hostnames in
httplib.HTTPConnection.init via a new validatehost helper to
prevent CRLF header injection (the glibc CVE-2016-10739 mitigation
shipped on RHEL 7+ is not present on CentOS 6 / Oracle Linux 6 ELS)
CVE-2018-1000030: cache the readahead buffer thread-locally inside
file_iternext to fix heap buffer corruption and crashes when multiple
threads iterate over the same file object