Fix for "Need encoding conversion for GIOChannel"

[HideToshi Tajima <tajima happy eng sun com>]

Hi,

I've posted a patch for one of the remaining 2.0 API bugs:
http://bugzilla.gnome.org/show_bug.cgi?id=52811, whose short summary
is "Need encoding conversion for GIOChannel".

The patch should give GIOChannel class the features listed below:

       * charset code conversion at read/write, read/write by chars
       * buffering 
       * blocking vs non-blocking (controled by *set_flags/get_flags)
       * Reading a file a line at a time
       * Reading a whole file at once
       * error handling with more error feedbacks	

A simple testcase is attached to the above bugzilla report. I've run
the test with this testcase on two Unix platforms - redhat linux6.2 Intel
and Solaris 8 sparc, and the patch seems to work well on both. I have to
say that win32 backend code is untested(more precisely unimplemented) - so
I wish to get someone who knows win32 have a look, test, and complete the
code.

A review comment will be highly welcome. Also, please let me know if there
is some process I should follow in order to get an approval to commit the
code change.

Regards,
Toshi