By Jarrett Renshaw and Nathan Layne PHILADELPHIA (Reuters) -A Pennsylvania court sided with Republicans in striking down a law on Friday that eliminated barriers to voting by mail, raising doubts over ballot access in the battleground state ahead of important election contests this year. The administration of Democratic Governor Tom Wolf immediately appealed the ruling, which deemed the law unconstitutional. That puts its implementation on hold while the Pennsylvania Supreme Court weighs the matter. Three Republican judges agreed with the GOP who had challenged the law, Act 77, saying the stat…