Prompt length calculation fails when UTF-8 is used within \[ \]

[Lasse Kärkkäinen]

Steps to reproduce: (using UTF-8 locales)

$ export PS1="\[\e]2;test Ä and Ö here\a\]prompt>"
prompt>abcdefgh    # Enter some alphabets and press Home
     ^ Cursor goes here, instead of
       ^ here where it should go.

Add more UTF-8 letters as non-printable characters in PS1 and the offset 
from the correct position gets bigger. Here it was two characters 
because of two "extra" bytes in the UTF-8 put in there.

I noticed that you have to type a right amount of characters to make 
Home key use the calculated prompt length. abcdefgh seems to work in 
this case, but if the prompt is modified, you may need to type more or 
less than that to see the effect.

Tested with versions:
GNU bash, version 4.0.0(2)-release (x86_64-unknown-linux-gnu)
GNU bash, version 3.2.48(1)-release (x86_64-pc-linux-gnu)