Removed.  ANSI C doesn't (explicitly) allow macro expansion in
arguments using `##'.
(FT2_PUBLIC_FILE, FT2_CONFIG_FILE, FT2_INTERNAL_FILE): Use directory
names directly.  Make them configurable.  Use `##' to strip leading
and trailing spaces from arguments.

* builds/unix/ft2unix.h: Adapted.

* src/base/ftsystem.c (ft_alloc, ft_realloc, ft_free, ft_io_stream,
ft_close_stream): Use FT_CALLBACK_DEF.

* builds/unix/ftsystem.c: Use new header scheme.
(FT_Done_Memory): Use free() from FT_Memory structure.

* src/base/ftinit.c, src/base/ftmac.c: Header scheme fixes.

* include/freetype/config/ft2build.h (FT2_CONFIG_ROOT,
FT2_PUBLIC_FILE, FT2_CONFIG_FILE, FT2_INTERNAL_FILE,
FT_SOURCE_FILE): Use `##' operator to be really ANSI C compliant.