Improve eglSwapBuffers error handling.

We now distinguish EGL_CONTEXT_LOST errors from
other kinds of errors. We return "true" if
the swap completes successfully, "false" if
the swap fails due to EGL_CONTEXT_LOST, and
throw a RuntimeException if the swap fails due
to any other cause.

If eglSwapBuffers succeeds, we now avoid calling
eglGetError at all, which means we avoid clearing
any EGL errors that might already have been
pending before eglSwapBuffers is called.