Before this fix, client tools (mysql_upgrade, mysqlcheck, mysqldump)
would try to process performance schema tables, leading to failures.

The fix is to align FIRST_PERFORMANCE_SCHEMA_VERSION to 5.5.3,
which is the version number of mysql-trunk where the
performance schema is first available.

Before this fix, the performance schema instrumentation
in mdl.h / mdl.cc was incomplete, causing:
- build warnings,
- no data collection for the performance schema

This fix:
- added instrumentation helpers for the new preferred
  reader read write lock, mysql_prlock_*
- implemented completely the performance schema
  instrumentation of mdl.h / mdl.cc

Set $glob_bindir, like $bindir in v2
Removed some obsolete IM code rather than changing it

Before this fix, mysql_upgrade would always drop and re create
the performance_schema database.
This in theory could destroy user data created using 5.1 or older versions.

With this fix, mysql_upgrade checks the content of the
performance_schema database before droping it.

Fix for BUG#51215 "log-error partially works with version 5.5": WL 4738 (reengineering of server variables)
had broken the 5.1 behaviour of --log-error: --log-error without argument sent to stderr instead of writing
to a file with an autogenerated name.

The unit test pfs_instr-t:
- generates a very long (10,000) bytes file name
- calls find_or_create_file.

This leads to a buffer overflow in mysys in my_realpath(),
because my_realpath and mysys file APIs in general do not
test for input parameters: mysys assumes every file name
is less that FN_REFLEN in length.

Calling find_or_create_file with a very long file name is likely
to happen when instrumenting third party code that does not use mysys,
so this test is legitimate.

The fix is to make find_or_create_file in the performance schema
more robust in this case.

The root cause of the failure is that when
Bug#51447 performance schema evil twin files
was fixed, instrumented file names got normalized.

The pfs-t unit test depends on this file normalization,
but it was not updated.

This fix aligns pfs-t.cc lookup_file_by_name()
with the logic in pfs_instr.cc find_or_create_file().

and "README" (header part: "This is a release of MySQL ...")
from "trunk" to "next-mr".

by adding the header part "This is MySQL ...".

the license remains to be the GPL Version 2, June 1991

This is *no* change in contents, the differences are formatting only
and an address update of the FSF. It continues to be Version 2, June 1991.

Bug#51676 Server crashes on SELECT, ORDER BY on 'utf8mb4' column
An additional fix. We should use 0xFFFD as a weight for supplementary
characters, not the "weight for character U+FFFD".

Using latin1 client character set for ASCII locales:
- because ascii is not a build-in character set
- for better backward compatibility

Bug#51675 Server crashes on inserting 4 byte char. after ALTER TABLE to 'utf8mb4' 
Bug#51676 Server crashes on SELECT, ORDER BY on 'utf8mb4' column