PHILADELPHIA — The Republican primary for Pennsylvania governor is coming down to the wire. In a nine-person race, no candidate is expected to get a majority of the vote in the May 17 election. But recent polling, both public surveys and campaigns’ internal polls, as well as interviews with GOP insiders point to a clear front-runner: state Sen. Doug Mastriano. Everyone else is playing catch-up, and while some Republicans are warning that Mastriano could cost the party up and down the ballot in the general election, his opponents haven’t coalesced behind a single alternative. Mastriano’s leadin…