too much at once; initialize calc.derivs attempt
add derivs calc code
calc.deriv/use.last.params fixes in progress
fixes for #166, calc.derivs; now passes R CMD check
implement convergence check control; update tests and documentation

(still need unit tests of convergence check control!)
Merge branch 'calc.derivs'

Conflicts:
	R/lmerControl.R
	R/optimizer.R
	inst/tests/test-lmer.R
	man/lmerControl.Rd
	man/merMod-class.Rd
Merge branch 'master' of ssh://github.com/lme4/lme4