Adding Chinese translation prepared by Liping Chen, MSU
Provide better solution to the numOfAttempts issue

 Insures that the number of attempts defined in the environment is correct.
 It is the sum of the number of incorrect attempts, the number of correct attempts
 and the number of ungraded attempts (which is 1 or 0 depending upon whether an
 answer has been submitted).
 The calculation is done in PG.pm
Merge branch 'release/2.7' of https://github.com/openwebwork/webwork2 into release/2.7
Merge pull request #81 from mgage/release/2.7

Fix off by one bug in number of attempts
Fix disappearing hidden sets.

caused because .hidden was not overriding the display mode for font.hidden
Also fixed the 90% width bug for the problem-content <div>
Merge pull request #82 from mgage/release/2.7

Fix problem-content width=90% bug; Fix disappearing hidden sets.
Define WEBWORK_DIRECTORY if it is not already defined.

Backported from develop
Fixes issue #16
Merge branch 'release/2.7' of https://github.com/openwebwork/webwork2 into release/2.7
Merge pull request #83 from mgage/release/2.7

Define Constants::WEBWORK_DIRECTORY from ENV{WEBWORK_ROOT} if it is not already defined.
Merge pull request #22 from openwebwork/release/2.7

Release/2.7
Make OPL the default library instead of NPL

This addresses issue #85
Use internal WWsafe.pm instead of system Safe.pm
Fix default address for libraries.

correct library to libraries
Obtain version number from file VERSION (variable name: $WW_VERSION)
Merge pull request #86 from openwebwork/hotfix1

Hotfix1
Update math4.css

Addressed bug 2647
Fixed broken disabled buttons