Fixes #11339 - ensure unique parameters before adding uniq index

[jlsherrill]

No description provided.

[domcleal]

Please note that tests are failing.

[jlsherrill]

Doh! Last minute change, updated!

[dLobatog]

Works well. However it worries me that the following code:

2.times do 
   foo = Parameter.new(:name => 'foo', :reference_id => 2)
   foo.type = 'DomainParameter'
   foo.save
end

Parameter.where(:name => 'foo') # this will return 2 values

still produces duplicates despite the unique index. Validations do actually run if you create the parameter using DomainParameter, etc... instead of setting the type manually.

update - I try to fix this on #2604

[dLobatog]

Merged as aabf3c2, thanks @jlsherrill!