Corretly sort requirement list
Dropped setting of PERLBREW_HOME

We don't use switch or init, where it would be needed, so setting it
would do more harm than good
Switching back to installing one module at a time

Sadly bulk installing modules will lead to strange 'Already tried
Foo::Bar' errors (cpanm bug?) and will keep install running way past
the point where breakage occured
Prereqs are already sorted now
Also drop PERLBREW_HOME fomr Mist::Context
Performance comparison for --branch and --parent