When built with the BUILD_STATIC knob, plugins are compiled statically in to the
mysqld binary, however, the installation process still creates the plugin
directory.  This directory remains empty and is not removed when the package is
deinstalled due to the expansion of %%PLUGINS%% to @comment.

===>  Installing for mysql-server-5.1.52
===>   mysql-server-5.1.52 depends on shared library: mysqlclient.16 - found
===>   Generating temporary packing list
===>  Checking if databases/mysql51-server already installed
===> Creating users and/or groups.
Using existing group `mysql'.
Using existing user `mysql'.
[removed]
Making install in archive
test -z "/usr/local/lib/mysql/plugin" || ../.././install-sh -c -d "/usr/local/lib/mysql/plugin"
Making install in blackhole
test -z "/usr/local/lib/mysql/plugin" || ../.././install-sh -c -d "/usr/local/lib/mysql/plugin"
Making install in csv
test -z "/usr/local/lib/mysql" || ../.././install-sh -c -d "/usr/local/lib/mysql"
Making install in federated
test -z "/usr/local/lib/mysql/plugin" || ../.././install-sh -c -d "/usr/local/lib/mysql/plugin"
Making install in heap
test -z "/usr/local/lib/mysql" || ../.././install-sh -c -d "/usr/local/lib/mysql"
 install  -o root -g wheel -m 444 'libheap.a' '/usr/local/lib/mysql/libheap.a'
 ranlib '/usr/local/lib/mysql/libheap.a'
Making install in innobase
test -z "/usr/local/lib/mysql/plugin" || ../.././install-sh -c -d "/usr/local/lib/mysql/plugin"

Though there is nothing to install in the above output, install-sh appears to
still create the directory.

Fix: Patch supplied.
How-To-Repeat: bender#	cd /usr/ports/databases/mysql51-server
bender#	make install clean BUILD_STATIC=YES
bender#	make deinstall
bender#	find /usr/local/lib/mysql/plugin
/usr/local/lib/mysql/plugin
bender#