avoid linking .git stuff in submodules

moved homeshick script so it is not linked in home.
fixed utils/fs.sh so it avoids linking .git stuff when a castle has submodules.
added a homesick alias in ~/.sourced/homeshick file, that should be
sourced by the shell.
support for oninstall and onupdate scripts

When a castle is cloned and has an oninstall.sh script on the castle
root, homeshick asks whether to run it.

When a castle is pulled and has an onupdate.sh script on the castle
root, homeshick asks whether to run it.
Merge branch 'master' of https://github.com/agvim/homeshick

merge together the reference branch