Simple patch for nextUTF8()

[Stefan Bidi]

I'm having to re-do a lot of the character encoding code in CFString
and while researching what base did I noticed that the nextUTF8 could
use some optimization.  I removed the while loop there and replaced it
with the macro I will be using in CFString.

Another change I made was remove an exception towards the end of the
function.  The exception above it already covers the case where (u >=
0xfdd0 && u <= 0xfdef).  Also, a surrogate is invalid in a UTF-8
string, the "invalid unicode code point" is a more appropriate
description here.

I didn't commit patch myself since I wanted to make sure other people
here agreed with it, and that there isn't anything I'm missing.  I ran
the testsuite and everything passed.

GSString_UTF8.patch
Description: Binary data