* methods/rred.cc:

* methods/rred.cc:
  - check return of writev() as gcc recommends
* methods/mirror.cc:
  - check return of chdir() as gcc recommends
* apt-pkg/deb/dpkgpm.cc:
  - check return of write() a gcc recommends
* apt-inst/deb/debfile.cc:
  - check return of chdir() as gcc recommends
* apt-inst/deb/dpkgdb.cc:
  - check return of chdir() as gcc recommends