relocatable activate as https://github.com/pypa/virtualenv/issues/11

[kra]

This implements the suggestion from #11 for activate.sh.

VIRTUAL_ENV is made dynamic, so activate will work with a relocated virtualenv.

Other activation scripts have not been changed.

[misaka]

This commit will break compatibility with zsh ($BASH_SOURCE is bash-specific) and with Mac OS X (readlink's -f option isn't supported on OS X ... and possibly on BSD in general).

I think the cd ... solution is probably a better one, although it's less efficient, but unfortunately I'm not sure what's the best way around the $BASH_SOURCE issue. In zsh $0 would work, so perhaps a zsh-specific script would be required.

[jpenney]

This works for both bash and zsh (tested on Linux/Mac OS/Cygwin) on paths with and without spaces in the name.

VIRTUAL_ENV="$(cd "$(dirname "${BASH_SOURCE:-0}")/.."; pwd)"

[carljm]

Closing as superseded by #236.