Assorted script fixes and memcached configuration instructions.

- Added memcached configuration instructions to documentation
- Added a cleanup script for the install/download directory
- Added a script to copy or append memcached settings in Vagrant
- Vagrant bootstrap.sh script installs wget now
- CentOS scl_install script installs wget now (This is supposed to be run before the dependency_redhat script, so it should cover the wget installation that dependency_redhat needs)
- Ubuntu dependency_ubuntu.py script installs wget now
- Added .gif files to .gitattributes

CentOS (x64) and Ubuntu (x86, x64) python scripts have been retested (Ubuntu was tested on x86 only, but the only arch-dependent code dealt with Python Imaging Library library locations and hasn't changed.)