Use m_asprintf() instead of nfmalloc() and string operations

This avoid the need to know the resulting string length beforehand, and
makes sure it's always going to get the right size. It also makes the
code way clearer.

Usage of nfmalloc() here was not appropriate anyway, as the variables
are only of temporary use, so switching to normal allocation gives
a side-effect “bug” fix.

dpkg-split/queue.c

@@ -174,11 +174,10 @@ void do_auto(const char *const *argv) {
     if (getc(part) != EOF) ohshit(_("part file `%.250s' has trailing garbage"),partfile);
     if (ferror(part)) rerr(partfile);
     fclose(part);
-    p = nfmalloc(strlen(opt_depotdir) + 50);
-    q = nfmalloc(strlen(opt_depotdir) + 200);
-    sprintf(p, "%st.%lx", opt_depotdir, (long)getpid());
-    sprintf(q, "%s%s.%lx.%x.%x", opt_depotdir, refi->md5sum,
-            refi->maxpartlen,refi->thispartn,refi->maxpartn);
+
+    m_asprintf(&p, "%st.%lx", opt_depotdir, (long)getpid());
+    m_asprintf(&q, "%s%s.%lx.%x.%x", opt_depotdir, refi->md5sum,
+               refi->maxpartlen, refi->thispartn, refi->maxpartn);
     part= fopen(p,"w");
     if (!part) ohshite(_("unable to open new depot file `%.250s'"),p);
     nr= fwrite(buffer,1,refi->filesize,part);
@@ -189,6 +188,8 @@ void do_auto(const char *const *argv) {
       ohshite(_("unable to sync file '%s'"), p);
     if (fclose(part)) werr(p);
     if (rename(p,q)) ohshite(_("unable to rename new depot file `%.250s' to `%.250s'"),p,q);
+    free(q);
+    free(p);
 
     printf(_("Part %d of package %s filed (still want "),refi->thispartn,refi->package);
     /* There are still some parts missing. */