added summary/description per package.

This reverts commit 5d6f3cebca77ee650e6cde3bd738d1fac0a8110c.

When restoring lastinx last_key.keyinfo must be updated as well. The
good example is in _ma_check_index().

The point of failure is extra(HA_EXTRA_NO_KEYREAD) in
ha_maria::get_auto_increment():

  1. extra(HA_EXTRA_KEYREAD) saves lastinx;
  2. maria_rkey() changes index, so the lastinx and last_key.keyinfo;
  3. extra(HA_EXTRA_NO_KEYREAD) restores lastinx but not
     last_key.keyinfo.

So we have discrepancy between lastinx and last_key.keyinfo after 3.

my_copy_fix_mb() passed MIN(src_length,dst_length) to
my_append_fix_badly_formed_tail(). It could break a multi-byte
character in the middle, which put the question mark to the
destination.

Fixing the code to pass the true src_length to
my_append_fix_badly_formed_tail().

There is a server startup option --gdb a.k.a. --debug-gdb that requests
signals to be set for more convenient debugging. Most notably, SIGINT
(ctrl-c) will not be ignored, and you will be able to interrupt the
execution of the server while GDB is attached to it.

When we are debugging, the signal handlers that would normally display
a terse stack trace are useless.

When we are debugging with rr, the signal handlers may interfere with
a SIGKILL that could be sent to the process by the environment, and ruin
the rr replay trace, due to a Linux kernel bug
https://lkml.org/lkml/2021/10/31/311

To be able to diagnose bugs in kill+restart tests, we may really need
both a trace before the SIGKILL and a trace of the failure after a
subsequent server startup. So, we had better avoid hitting the problem
by simply not installing those signal handlers.