Do not show the PID of the application at startup

Any warning message from g_log() will show the PID, and it is otherwise
not that useful.
Check for gdk-pixbuf-pixdata in configure

The gdk-pixbuf-pixdata tool is required for glib-compile-resources when
using the to-pixdata option.
Fix a MinGW build failure in EtBrowser
Update Windows installer script

Include complete Adwaita icon theme. Include winpthread DLL.