Previously, SystemCommand commands and arguments were processed as
strings which caused problems during shell interpretation if the
arguments were not escaped properly. Now all commands are expressed
as arrays and no longer require their arguments to be escaped.
Additionally, stderr and stdout could have been interleaved in the
past and now they are always separated.
- do not remove *all* symlinks from referenced dirs, only broken ones
- restore dir permission after use so we don't leave behind 777 dirs
- add some better testing around `Cask::Pkg`
- clean up `FakeSystemCommand` interface in tests
refs #1274
Roland Walker