[PATCH 2/N] cleanup return values of convert_string, push_utf8, and friends

Here is the second round of fixes for the patch set we discussed that  
cleans up the return values in charcnv.c.  This one fixes the callers  
of convert_string_allocate as well as their callers.  This patch  
turned out to be a bit larger then I wanted, but it was much cleaner  
to just fix all callers at the same time.

-Tim

Tim Prouty | Software Development Engineer
Isilon Systems
www.isilon.com