Merge pull request #54 from Dick-Lane/master

Ficks spelink erur
Switch to math objects.
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
Fixed bug 2890
Fix bug 2893
New lin alg problems.
Merge branch 'master' of git://github.com/openwebwork/webwork-open-problem-library
Fix bug 2892, and convert to math object
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
Tiny fix.
Fixing units link
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
Slightly modified version added.
Fixing permissions and improving look of a problem.
Merge branch 'master' of github.com:openwebwork/webwork-open-problem-library
Fix bug 2901
clean up coding
Redefine domain of function evaluation

Context()->variables->set(x=>{limits=>[1,5]});
cosmetic: displaystyle for rational function, different size parentheses