Improve relative path resolution (retry)

[michaelsternberg]

These changes were inspired by issues found in ATARI NOS when trying to open, launch, copy files using relative paths.

• Fixed a bug in function util_get_canonical_path
  • Previous logic always exited with trailing slash, not good if input ends with a filename. If trailing slash found in input, then it will exist in output. If not then no slash in output.
  • Corrected mistake with condition involving C++ string length.
  • Renamed input arg from prefix to path throughout.
• In peoples_url_parser, added call to util_get_canonical_path in place of an existing string replace function that substituted '//' with '/'. This should resolve relative paths in general for all protocols.

[tschak909]

Thank you!