[ft] FT_* error messages

[Stefano Sabatini]

Hi all,

fterrid.h contains a list of error messages defines, and FT_*
functions return such error messages, but doesn't seem to be a way to
convert these error codes in corresponding strings to be delivered to
the user rather than the error code itself.

It would be nice to provide some function to translate a-la strerr
those error codes, in this way application won't have to provide
themselves such messages to the user.

Regards.