BM Duplicate projects in attach wizard

[mifistor_x]

BOINC manager.

Start "Attach to project" wizard.

On page "Project selection" :

step 1: projects == X,

step 2: press "<Back" ("Attach to project" page) then "Next>" ("Project selection" page), projects == 2*X

...

step n: press "<Back" ("Attach to project" page) then "Next>" ("Project selection" page), projects == n*X

[romw]

(In [12847]) - fixes #241: BOINC Manager should only display one of each

project, no mater how many time you switch to and from the page.

clientgui/

ProjectInfoPage?.cpp, .h