Show all untracked files, not just directories

By default, git will only show a directory with untracked files in it,
but what I want to know is which files are untracked (this especially
makes more sense as git doesn't actually track directories, just files).
Fortunately, there's a git-config(1) for that!
Recognize .spreadsheet/.prawn as Ruby in Vim

Using sinatra-prawn* and sinatra-spreadsheet**, it's fairly easy to add
in views that output PDFs and (surprise) spreadsheets - the view files
are ultimately just Ruby code, though, so we should use Ruby syntax
highlighting/etc. on them.
Fix a bug during `rcfiles save` w/untracked files

Untracked files weren't saving properly because the new `__git` method
returns full output, not individual lines, so anything more than one new
untracked file, and no new untracked files would be added to the commit.
Silence certain Perl::Critic warnings on rcfiles

I finally enabled Perl::Critic, only to find that subroutine prototypes
are discouraged! That, in turn, is discouraging! I can understand the
long-term reasoning, but for now this script is a one-off binary and I
think the layout works better, so we're ignoring that.

Additionally, the `no strict 'refs';` line in `bin/rcfiles` is necessary
for what I'm doing there, and at the very least very intentional and
very limited, so I've silenced the one warning generated by that line.
Add `mergehist` subcommand to `rcfiles`

See `rcfiles help mergehist` for full details on what this function does
(hint: it merges history files, but OH SO MUCH MORE).