A.J. Jenkins may start at receiver for Niners in preseason opener

The 49ers didn’t need much from 2012 first-round receiver A.J. Jenkins during his rookie season..  Which is good, because they didn’t get much.  They got so little that Matt Maiocco of CSNBayArea.com recently suggested on PFT Live that, if Jenkins hadn’t been a first-round draft pick, he would have gotten cut last year. This year,…