Shell-escape tasks before passing them to capistrano

When I try to to use the `invoke` command I have the problem that the `COMMAND='some command'` is not being escaped before passed to capistrano.
Let's say I run:
```bash
pulsar -v -l trace app env invoke COMMAND='uname -a'
```
Pulsar will eventually run:
```bash
bundle exec cap CONFIG_PATH=/tmp/pulsar/conf-repo-2013-07-23-183838-s5061 --file /tmp/pulsar/capfile-2013-07-23-183838-s5061 invoke COMMAND=uname -a
```
which doesn't work and results in:
```
/usr/local/homebrew/Cellar/ruby/2.0.0-p247/lib/ruby/gems/2.0.0/gems/capistrano-2.15.5/lib/capistrano/cli/options.rb:154:in `parse_options!': invalid option: -a (OptionParser::InvalidOption)
	from /usr/local/homebrew/Cellar/ruby/2.0.0-p247/lib/ruby/gems/2.0.0/gems/capistrano-2.15.5/lib/capistrano/cli/options.rb:15:in `parse'
	from /usr/local/homebrew/Cellar/ruby/2.0.0-p247/lib/ruby/gems/2.0.0/gems/capistrano-2.15.5/lib/capistrano/cli/execute.rb:14:in `execute'
	from /usr/local/homebrew/Cellar/ruby/2.0.0-p247/lib/ruby/gems/2.0.0/gems/capistrano-2.15.5/bin/cap:4:in `<top (required)>'
	from /usr/local/opt/ruby/bin/cap:23:in `load'
	from /usr/local/opt/ruby/bin/cap:23:in `<main>'
```