Bug #39641 mysql_config --plugindir links to /usr/local/mysql/lib/plugin in tar.gz packages

Description:
mysql_config --plugindir outputs /usr/local/mysql/lib/plugin when using *tar.gz package instead of using installation directory

How to repeat:
$/users/ssmirnova/mysql-5.1.28-rc-linux-i686-glibc23/bin/mysql_config 
Usage: /users/ssmirnova/mysql-5.1.28-rc-linux-i686-glibc23/bin/mysql_config [OPTIONS]
Options:
        --cflags         [-I/users/ssmirnova/mysql-5.1.28-rc-linux-i686-glibc23/include  -g -DUNIV_LINUX]
        --include        [-I/users/ssmirnova/mysql-5.1.28-rc-linux-i686-glibc23/include]
        --libs           [-rdynamic -L/users/ssmirnova/mysql-5.1.28-rc-linux-i686-glibc23/lib -lmysqlclient -lz -lcrypt -lnsl -lm -lmygcc]
        --libs_r         [-rdynamic -L/users/ssmirnova/mysql-5.1.28-rc-linux-i686-glibc23/lib -lmysqlclient_r -lz -lpthread -lcrypt -lnsl -lm -lpthread -lmygcc]
        --plugindir      [/usr/local/mysql/lib/plugin]
        --socket         [/tmp/mysql.sock]
        --port           [0]
        --version        [5.1.28-rc]
        --libmysqld-libs [-rdynamic -L/users/ssmirnova/mysql-5.1.28-rc-linux-i686-glibc23/lib -lmysqld -lz -lpthread -lcrypt -lnsl -lm -lpthread -lrt -lmygcc]

Suggested fix:
Link plugindir to INSTALLATIION_DIRECTORY/lib/plugin as other parameters do.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/85185

3142 Jonathan Perkin	2009-09-30
      bug#39641: mysql_config --plugindir links to /usr/local/mysql/lib/plugin in
                 tar.gz packages
      
      Do the fix_path kludge for the plugin directory.

I'll take this one as I implemented the plugindir in the first place, made Kent reviewer instead.

Fix race condition in bug system.

Fixed long ago by the fix for bug#52737.