GitIgnore *.log, *.msi
Added actual list of supported OSTYPES for VirtualBox 4.2.18r88780

You can easily get this list with your installed version of VirtualBox
by running the command "vboxmanage list ostypes".
Added template for CentOS 6.3 32-Bit box.
Added template for CentOS 6.3 64-Bit box.
Added template for CentOS 6.4 32-Bit box.
Added template for CentOS 6.4 64-Bit box.
Added template for Ubuntu 12.04.1 32-Bit box.
Added template for Ubuntu 12.04.1 64-Bit box.
Added template for Windows 7 SP1 64-Bit box.
Added use of a local PACKER_CACHE_DIR

If there is no global PACKER_CACHE_DIR set, then use a local cache dir
".\packer_cache" for all your build.