Added auto-generated tag files.

Anything matched by `*.un~` will also be matched by the last rule, `*~`.

The old pattern was too broad and was making VIM ignore Scheme (*.scm) files.
Now it only matches files that start with . or _.

.*.s[a-w][a-z] matches named swap files.
.s[a-w][a-z] matches unnamed swap files.

Vim creates buffer swapfiles starting at .swp for buffers that are
active but untitled and unsaved.

Changed line matching vim swapfiles to use all names it will create as described in http://vimdoc.sourceforge.net/htmldoc/recover.html#E326

Include .netrwhist, the user's history and potential privacy concern. See: http://stackoverflow.com/questions/9850360/