Wrap commit message body at 72 characters

This is kinda aggressive, but it is reasoned in famous Tim Pope's blog
post:
http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html

It is also on the Qt Commit Policy, so is easier to set up globally...
Add alias for annoyingly long xdg-open
Fix breakindentopt length calculation
Increase solarized_visibility to "normal"
Change 'expandtab' default

Use expandtab by default, since is what most projects I work on use
anyway. Fine tune for Makefiles for now. Pending to evaluate vim-sleuth
and see how well works with C++.