spec/utils/resources.use() prepares a fresh copy of resources

also renames dot_git to .git, as there may be no .git directories in a git
repository (they would be considered submodules)
Added repo.git and sites/test for specs
fixed cwd property of ShellTask
Fixed Task.runNested() not passing along result
Added Task.prototype.exec() shorthand to execute shell commands
Implemented basic site loader