Ensure all v8 libraries are copied in README; sanity check in config.m4.

The latest versions of v8 build libicu as well.  If this isn't copied to
the lib directory, then the v8 version check fails (with a link error).
Ensure that this is caught at configuration time.
Merge pull request #46 from cscott/more-build-tweaks

Ensure all v8 libraries are copied in README; sanity check in config.m4.