dbghelp: SymFindFileInPath and PDB

- implemented correct lookup when SymFindFileInPath is called to find
  a PDB file
- added pdb_fetch_file_info to gather relevant information
- when looking for a PDB file (from a .EXE or a .DLL), now using
  SymFindFileInPath to locate the PDB file with the correct
  information
4 files changed