slowparse errors are now stored as raw i18n json bundles in optimized builds.

previously, their raw HTML was being parsed into i18n bundle format
at runtime.
refactorings to make l10n infrastructure easier to understand.
moved build-i18n.js and build-require.js into a 'bin' directory.
added node-tap tests for build-i18n.js, and fixed a bug in html-to-i18n.js.
'npm test' now also tests unoptimized and optimized qunit tests, build step.
removed self-test from bin/build-require.js, since node-tap tests obviate it.