Merge branch 'ab/struct-init'

Code cleanup around struct_type_init() functions. * ab/struct-init: string-list.h users: change to use *_{nodup,dup}() string-list.[ch]: add a string_list_init_{nodup,dup}() dir.[ch]: replace dir_init() with DIR_INIT *.c *_init(): define in terms of corresponding *_INIT macro *.h: move some *_INIT to designated initializers