quotearg.c doesn't compile on non-multibyte systems

[Bryan Henderson]

When config.h indicates that the mbstate_t type doesn't exist, by
not defining the various macros that declare presence of multibyte
facilities on the system, quotearg.c still declares a data type
as type mbstate_t and tries to do multibyte stuff.

Other parts of the package use ifdefs so they compile on such systems.

I don't know enough about multibyte functions to know the right fix 
for this; I just deleted the whole block of code that includes the
reference to mbstate_t and it seemed to be OK.

-- 
Bryan Henderson                                    Phone 408-621-2000
San Jose, California