Run `tap --repair` as part of `prune`

And by extension, `cleanup`.

Fixes #18658.
Improved formula attribute validation

The initializer for Formula does a number of validations, but it does
them in a weird order, and some attributes aren't validated under
certain circumstances. This became even more of a mess when most
software package attributes were moved into the SoftwareSpec class.

This commit removes the last vestiges of storing these attributes as
instance variables. In particular, it eliminates #set_instance_variable
and #validate_variable, replacing them with methods that operate on
SoftwareSpec instances, and generate more useful errors.

Doing these validations unconditionally in the initializer means we bail
out much earlier if the formula has invalid attributes or is not fully
specified, and no longer need to validate in #prefix.

Technically we don't need to validate in #brew either, but we continue
to do so anyway as a safety measure, and because we cannot enforce calls
to super in subclasses.
Allow "devel-only" formulae

It seems only natural that this should be possible, or at the very
least, it should not result in calling methods on nil.
Add tests for formula spec selection

These tests document the relative precedence of the stable, bottle,
devel, and head specifications, and the conditions that can influence
which is selected (e.g. command-line flags).
Raise a useful exception for incomplete formulae
Make a specific assertion in this test
Remove obsolete tests

This behavior is now tested at more appropriate levels in
test_software_spec, test_formula_spec_selection, and
test_formula_validation.
Use assert_operator
Remove extra require
OpenSSL: enable ec_nistp_64_gcc_128 option on 64-bit machines

This is supposed to increase speed dramatically...

Closes #19064.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
spin: install ispin

Closes #19044.
rrdtool: use stdenv to support custom perl and ruby

Closes #19018.
New visualization for brew deps --tree

Closes #18835.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
New formula: libtar

libtar provides a C interface to tar files. It installs include and
library files as well as an executable called libtar, which provides
similar functionality to tar and gnu-tar. I think there should be
no conflicts since the executable has a different name.

Closes #18780.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
New formula: libusbx 1.0.14

Added homebrew formula for the popular user-space USB library, libusbx 1.0.14

Closes #17186.
Closes #18452.

Signed-off-by: Jack Nagel <jacknagel@gmail.com>
wireshark: modernize style
libusb: fix typo
cassandra 1.2.4

Closes #19187.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
vim 7.3.891

Closes #19188.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
libmatroska 1.4.0

Closes #19190.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>