Fixing a problem with a new version of the Matrix package.

Advancing to version 1.2-2.

Also:
- Adding README.md to .Rbuildignore.
- Fixing some typos in the vignette.
Version 1.2-3.

- Removing all ::: calls.
- Moving all packages except Matrix and lme4 to imports.
- Cleaning up man pages.
- Adding plot method for rlmerMod objects.
Version 1.2-4.

Aligning methods with lme4 1.1
- Many more methods to use for rlmerMod objects,
  almost all that are available for merMod objects
  are also available, notably also predict().
- The output of coef() changed and is now the same
  as for merMod objects.
- Updated tests and made them more strict.
Version 1.2-5.

Improving help.
- Cleaned and compacted package documentation.
- Added links to documentation to most of the
  S3methods that are exported.
- Minimal copying of functions from lme4.