More defensive handling of pluginInfo
Add support for platform dependent high resolution performance timers

For profiling filter performance
Add performance measurement features

This is an experimental module to help us measure the performance of
the refresh cycle and the filter mechanism. Not intended to replace the
performance measurement features in browser developer tools, just to
make it easier to automate performance checks cross-browser.

The immediate purpose is to help in refactoring the filter mechanism.
The recent change to encapsulate the wiki store “tiddlers” object has
hurt the performance of filters, and it’s going to be helpful to have
decent measurements while refactoring that code.

I’m still not convinced that this stuff should be in the core, and may
well end up removing it after the present refactoring cycle.