remove old ACTIVE file
rename plugins/holland.backup.mysqldump -> plugins/mysql
rename package holland.backup.mysqldump -> holland.mysql.mysqldump

This moves the mysqldump plugin until the holland.mysql namespace
as part of the plugin consolidation branch.
merge holland.lib.mysql into mysql plugin package
merge holland.backup.xtrabackup into mysql plugin package
merge holland.backup.delphini into mysql plugin package
rename holland.lib.lvm to lvm
rename holland.lib.common to common
merge holland.backup.mysql_lvm into mysql plugin package

mysql lvm backup plugins now are located under the
holland.mysql.lvm namespace.
rename holland.backup.pgdump -> pgsql
update plugins/README to reflect new plugin structure
move holland.backup.script under common plugin package
move holland.backup.{sqlite,random} to example plugin package