core: Use G_SEARCHPATH_SEPARATOR_S to separate paths
core: Use G_SEARCHPATH_SEPARATOR_S to separate paths

Currently, it means in Unix ":" will be used as the separator for the list of
paths to search for plugins, while in Windows it will be ";".

Signed-off-by: Juan A. Suarez Romero <af79b5692270b306571bb1d8bbe0285ae3ac93d9@igalia.com>

grilofw/grilo,jasuarez/grilo,jasuarez/grilo,GNOME/grilo,kyoushuu/grilo,GNOME/grilo,grilofw/grilo,MathieuDuponchelle/grilo,MathieuDuponchelle/grilo,kyoushuu/grilo,kyoushuu/grilo,MathieuDuponchelle/grilo,jasuarez/grilo,kyoushuu/grilo,grilofw/grilo