Namespaces initialisation bug

is_mw114 is set to be True for sites with mediawiki >= 1.14.
Those sites use Image namespace, rather than File.  The boolean
needs to be reversed.

Also, when adding aliases, do not add an alias if it is already
in the object.

Bug: 69278
Change-Id: Id85dea19554450f387c13f68f73ae54eeeaf941c
Merge "Namespaces initialisation bug"