making sure that plugin works without configuration file. Most of plugin

making sure that plugin works without configuration file. Most of plugin
configuration options are about tuning plugin and not about required site
specific changes.

optimized sqgetGlobalVar and include calls.

updated some docs.

git-svn-id: https://svn.code.sf.net/p/squirrelmail/code/trunk/squirrelmail@9400 7612ce4b-ef26-0410-bec9-ea0150e637f0