Fixed "gimpicons.c:30:45: fatal error: icons/Default/gimp-icon-pixbufs.c:
No such file or directory" after commits :
ee512b610dfa9e5b8f98
Fixed "ln: failed to create symbolic link ‘12/gimp-default-colors.png’:
File exists" by forcing new symlinking on creating get-default-colors.png
for Symbolic-inverted to prevent error during make.
Create GIMP_CONFIG_DEFAULT_(ICON_)?THEME in gimpguiconfig.h to set
defaults in a single place, except for libgimpwidgets/ which cannot
include from app/.