- Based on Fedor Karpelevitch's formpost path basename patch, file parts in

  formposts no longer include the path part. If you _really_ want them, you
  must provide your preferred full file name with CURLFORM_FILENAME.

  Added detection for libgen.h and basename() to configure. My custom
  basename() replacement function for systems without it, might be a bit too
  naive...

  Updated 6 test cases to make them work with the stripped paths.