Disallow 100% Percent Complete if there are open issues a task

[#1]

Description - I spent several days and even posted to the community to try to figure out why Can Start was false on some follow-on tasks. Come to find out there is a sneaky little inconsistency in task status behavior.

Why is this feature important to you - There are two reasons:

1. We rely a fair amount on the Percent Complete field instead of status because it adds more context to work in progress. When we see Percent Complete is 100%, we assume that the task is complete.
2. When a project has outstanding issues, we can't change the status to Complete. Therefore, any field that indicates a task is complete (or greatly implies) should follow the same behavior as a project because it's darn helpful for quality control.

How would you like the feature to work - If a user tries to set Percent Complete to 100%, present them with an error message describing alerting the user that there are open issues and default the value to the previous value.

Current Behaviour - A user can set Percent Complete to 100% and the task remains In Progress.