Actually, I'm turning this function into a macro as filename,
function name and line number needs to be passed. The new
function virAsprintfInternal is introduced with the extended set
of arguments.
If the creation of the commandline failed, libvirt always reported "out
of memory" from the virCommandToString function rather than the proper
error that happened in virStorageBackendCreateQemuImgCmd. Error out
earlier.
The source code base needs to be adapted as well. Some files
include virutil.h just for the string related functions (here,
the include is substituted to match the new file), some include
virutil.h without any need (here, the include is removed), and
some require both.
