[NEXUS-6708] Allow only one obr.xml group merge at one time

commit 4a7081de6795d369adebf6d59ab03a4e4be3c4e4
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Fri Nov 28 16:10:17 2014 +0200

    [NEXUS-6708] Reuse obr UID

commit e82a5ab22083b4e82b68fecdc88536b5d3111b42
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Fri Nov 28 12:57:03 2014 +0200

    [NEXUS-6708] No need to recalculate modified field

commit 0ebf7506bf2bf0c62e500e2608f02ad91374983f
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Fri Nov 28 12:32:36 2014 +0200

    [NEXUS-6708] Allow only one orb.xml group merge at one time

    + Double check merging condition

commit 811efce74866f64b01f3680e03351cb75f052e26
Author: Alin Dreghiciu <adreghiciu@gmail.com>
Date:   Fri Nov 28 12:17:48 2014 +0200

    [NEXUS-6708] Do not check if item is expired since item is always up to date

    Since we are retrieving the item, if item is expired Nexus will go remote and by the time we get to the item is always up to date