* plugin sandboxing
* remove unused type
* better symlink handling, better remounting, better test, whitespace
fixes, and comment on the remounting
* fix test compile error
* big simplification for getting mount flags
* mask statfs flags to the ones we're interested in
* tie back-end plugins together
* fix comment typo
* add tests and a bit of polish
* tests and polish
* add test, don't let backend executable paths escape the plugin directory
* Implement experimental REST API endpoints for plugins
* Updates per feedback and rebase
* Update tests
* Further updates
* Update extraction of plugins
* Use OS temp dir for plugins instead of search path
* Fail extraction on paths that attempt to traverse upward
* Update pluginenv ActivePlugins()
* begin backend plugin wip
* flesh out rpcplugin. everything done except for minor supervisor stubs
* done with basic plugin infrastructure
* simplify tests
* remove unused test lines
