The 'not dead yet' release

The 'not dead yet' release

* add hook for MarkInstall and MarkDelete (closes: #470035)
* add the various foldmarkers in apt-pkg & cmdline (no code change)
* versions with a pin of -1 shouldn't be a candidate (Closes: #355237)
* prefer mmap as memory allocator in MMap instead of a static char
  array which can (at least in theory) grow dynamic
* eliminate (hopefully all) segfaults in pkgcachegen.cc and mmap.cc
  which can arise if cache doesn't fit into the mmap (Closes: #535218)
* display warnings instead of errors if the parts dirs doesn't exist
* honor the dpkg hold state in new Marker hooks (closes: #64141)