Move disabled autocmd to ftplugin

Might as well turn this on for svn, but keep disabled for text. Now it's
in the right place (where I'm likely to look for it).
Make fc always pretty and work in cygwin

fc doesn't get any windows path translation, so vim expects /tmp to
be cygwin's unix /tmp. Link them together in the firstsetup.

Remove the redundant remove_junction block in windows_links. It's just a
copy of the create_junction. Add a comment explaining how to remove.

Use the sh filetype when editing an fc file.

Also use autocmd consistently.