support also <name>=<factory statement> in the mappings

Support also <name>=<factory statement> in the mappings, but you have to use ';' instead of ':' in the factory statement since the ':' is already used by the mapping.

Example:
       --PO 'map=.*_mm.*/FR_data:r_fake_mu[1,0,10]' \
       --PO 'map=.*_ee.*/FR_data:r_fake_el[1,0,10]' \
       --PO 'map=.*_em.*/FR_data:r_fake_em=expr;;r_fake_em("0.45*@0+0.55*@1",r_fake_mu,r_fake_el)' \
scales the FR_data using r_fake_mu in the mm modes,  r_fake_el in the ee modes and a linear combination of the two in the em mode.

Factory statements are to be executed after all the doVar statements (this will be put in a second commit but in this same branch, and so on the same request - don't merge this pull request until you see that one too)

       Giovanni