Added support for plugin debug messages and better error reporting
when something goes wrong during start up of SLPlugin.
Also added more debug output regarding general plugin messages
as well as debug output related to AIFilePicker.
Add back fixes that were in Singularity (in indra/media_plugins) but not
in imprudence.
Also:
Add "shutdown" plugin message and terminate file picker plugins cleanly.
The DSO (libbasic_plugin_filepicker.so) now tells the child process /
plugin loader (SLPlugin) to terminate (using the 'shutdown' message),
and AIFilePicker::finish_impl destroys the plugin object on the viewer
side when it's ... finished thus.
Also added a large comment that gives an overview of all classes
involved on the viewer side.
Additional fixes for filepicker.
Plugin refactor bug fix: mDeleteMe was uninitialized in AIPluginFilePicker.
This commit contains all changes, except those in indra/media_plugins
(which was renamed to indra/plugins) and indra/llplugin.
However, it does contain the (new) file
indra/plugins/filepicker/basic_plugin_filepicker.cpp
