[xml] potential problem in trio.c

[robert <robert xml 00008 org>]

Browsing through the code of trio.c (libxml2-2.3.9), I stumbled upon
the implementations of trio_asprintf and trio_vasprintf, which both use
TrioOutStreamStringDynamic().

The latter (re)allocates buffers using malloc() and realloc(), instead of
libxml's own memory-handlers xmlMalloc and xmlRealloc, which might pose
potential problems with projects defining their own memory-allocation
routines (like mine).

The same goes for trio_(un)register(), by the way.

                                                                   robert