freezed win32: put gspawn helper exe into lib/
The original placement in installation root was developed for earlier glib, and doesn't work for current mingw-w64-x86_64-glib2 2.58.1-1 (actually it breaked several versions ago). This prevents opening help from meld, since this uses external process execution, like #197 (closed)
Also looking at the previous code version I found that it had typo in the comment describing return value format. It's fixed now.