Add get_vaddr to RBinPlugin and fix vaddr calculation for PE files

This patch fixes the issue https://github.com/radare/radare2/issues/365 and makes test https://github.com/radare/r2-regressions/commit/7062c508b1a10d57daad87ad97eb70577ef4b29b succeed (BROKEN flag no longer needed), and doesn't break anything else in r2-regressions.