User should not be able to share a plan with him/herself

[stephaniesimms]

I accidentally invited myself to collaborate on a plan (same user account) and was able to do so. Now I receive two email notices for every action taken on the plan. I cannot remove myself (this is working as expected, but I should not be able to invite myself in the first place). In addition, I have two copies of the same plan on My Plans page (second screenshot).

[stephaniesimms]

accidentally closed

[jollopre]

The message provided when user tries to share plan with (him|her)self is:

Impossible sharing plan with someone@somewhere.com since that email matches with the owner of the plan

[stephaniesimms]

on Roadmap stage I just shared another plan with myself (screenshot below)

[sjDCC]

Fixed on both dmponline-test and staging. Generates correct error message