VHD: Fix locale aware character encoding handling

VHD: Fix locale aware character encoding handling

ASCII is 7 bit only, which does not work in UTF-8 environments:
> failed to read parent name

Setup locale in vhd-util to parse LC_CTYPE and use the right codeset
when doing file name encoding and decoding.

Increase allocation for UTF-8 buffer as one UTF-16 character might use
twice as much space in UTF-8 (or more).

Don't check outbytesleft==0 as one UTF-8 characters get encoded into
1..8 bytes, so it's perfectly fine (and expected) for the output to have
remaining bytes left.

Test-case:
$ ./vhd-util create -n ä.vhd -s 1
$ ./vhd-util snapshot -n snap.vhd -p ä.vhd ; echo $?

See
<http://unix.stackexchange.com/questions/48689/effect-of-lang-on-terminal>
for more information about the details of handling the encoding right.

Signed-off-by: Philipp Hahn <hahn@univention.de>
Acked-by: Ian Campbell <ian.campbell@citrix.com>