Post-push fixes making it work on pushbuild's valgrind host, and clarifying the output.

BUG#39008 Additional fix after review, remove files that could potentially be set to path outside datadir

BUG#38559 Annoying cygwin problem fixed by resolving  pid->winpid before kill instead of just after fork

WL4189 Add Handles.pm and use it from My::File::Path to show open handles. Rewrite rmtree to use File::Find so we can get better debug printouts when something fails

Disable the test case on valgrind. This is a backport to 5.1-rpl of
something that already exists in 5.1 main.

Rotate event is automatically generated and written when rotating binary
log or relay log. Rotate events for relay logs are usually ignored by slave
SQL thread becuase they have the same server id as that of the slave.
However, if --replicate-same-server-id is enabled, rotate event
for relay log would be treated as if it's a rotate event from master, and
would be executed by slave to update the rli->group_master_log_name and
rli->group_master_log_pos to a wrong value and cause the MASTER_POS_WAIT
function to fail and return NULL.

This patch fixed this problem by setting a flag bit (LOG_EVENT_RELAY_LOG_F)
in the event to tell the SQL thread to ignore these Rotate events generated
for relay logs.

This patch also added another binlog event flag bit (LOG_EVENT_ARTIFICIAL_F)
to distinquish faked events, the method used before this was by checking if
log_pos was zero.

Memoize functions that converts between different paths, a given input string will always return the same output. This save a lot of calls to cygpath for example