Fix 6 failing user spec tests

Fixes the following spec failures:

```
 1) User should create a new instance given a valid attribute
    Failure/Error: User.create!(@attr)
    ActiveRecord::RecordInvalid:
      Validation failed: Username can't be blank
    # ./spec/models/user_spec.rb:30

 2) User should reject duplicate email addresses
    Failure/Error: User.create!(@attr)
    ActiveRecord::RecordInvalid:
      Validation failed: Username can't be blank
    # ./spec/models/user_spec.rb:50

 3) User should accept valid email addresses
    Failure/Error: valid_email_user.should be_valid
      expected valid? to return true, got false
    # ./spec/models/user_spec.rb:37
    # ./spec/models/user_spec.rb:35:in `each'
    # ./spec/models/user_spec.rb:35

 4) User should reject email addresses identical up to case
    Failure/Error: User.create!(@attr.merge(:email => upcased_email))
    ActiveRecord::RecordInvalid:
      Validation failed: Username can't be blank
    # ./spec/models/user_spec.rb:57

 5) User password encryption should have an encrypted password attribute
    Failure/Error: @user = User.create!(@attr)
    ActiveRecord::RecordInvalid:
      Validation failed: Username can't be blank
    # ./spec/models/user_spec.rb:100

 6) User password encryption should set the encrypted password attribute
    Failure/Error: @user = User.create!(@attr)
    ActiveRecord::RecordInvalid:
      Validation failed: Username can't be blank
    # ./spec/models/user_spec.rb:100
```
Merge pull request #335 from jamestyj/jamestyj-user-spec-fix

Fix 6 failing user spec tests