`API functions' are functions tagged with `FT_EXPORT_DEF'.
Besides trivial fixes, the following changes are included, too.
* src/base/ftbdf.c (FT_Get_BDF_Charset_ID, FT_Get_BDF_Property): Set
error code if no service is available.
* src/base/ftinit.c (FT_Done_FreeType): Change return value for
invalid `library' parameter to `Invalid_Library_Handle'.
* src/base/ftobjs.c (FT_New_Size): Change return value for invalid
`asize' parameter to `Invalid_Argument'.
* src/base/ftoutln.c (FT_Outline_Copy): Change return value for
invalid `source' and `target' parameters to `Invalid_Outline'.
(FT_Outline_Done_Internal): Change return value for invalid
`outline' parameter to `Invalid_Outline'.
This is essentially a mechanical conversion, adding inclusion of
`FT_INTERNAL_DEBUG_H' where necessary, and providing the macros for
stand-alone compiling modes of the rasterizer modules.
To convert the remaining occurrences of FT_Err_XXX and friends it is
necessary to rewrite the code. Note, however, that it doesn't harm
if some cases are not handled since FT_THROW is a no-op.