Previously, FreeType misleadingly returned
FT_Err_Unknown_File_Format if a module was missing (or a test was
missing completely).

* include/freetype/fterrdef.h (FT_Err_Missing_Module): Define.

* src/cff/cffobjs.c (cff_face_init), src/cid/cidobjs.c
(cid_face_init), src/sfnt/sfobjs.c (sfnt_init_face),
src/truetype/ttobjs.c (tt_face_init), src/type1/t1objs.c
(T1_Face_Init), src/type42/t42objs.c (T42_Face_Init,
T42_Driver_Init): Updated.

* src/type1/t1afm.c (T1_Read_Metrics), src/type/t1objs.c
(T1_Face_Init), src/type42/t42objs.c (T42_Face_Init): Remove now
redundant test for `psaux'.