Boost: enforce '--with-mpi' with '--without-single'

* Building MPI support for both single and multi-threaded flavors will
  result in duplicated rules for mpi.so.  Upstream bug report
  https://svn.boost.org/trac/boost/ticket/8841.
* Require '--with-mpi' be used together with '--without-single' until
  this is fixed.
brew reinstall: Reuse options from last time

Now, we can finally stop stuggesting to
    `brew rm <foo>` and then `brew install <foo> <with-your-preferred options>

So `brew reinstall` will honor all options that have been recorded
into the INSTALL_RECEIPT.json plus if `--build-bottle` was used.
Unlinked brewed python -> use system python

Up to now a brewed Python, even if not linked, was preferred over
and external Python, so that you had to completely `brew rm python`
to have a formula link against external (mostly system) Python.

From now on it is okay to `brew unlink python`.
unpack: ensure $VERBOSE is restored
unpack: remove dead code
unpack: use ARGV.value
chruby: Fix typo and update dotfiles in caveats.

Closes #21903.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
SonarQube 3.7

Closes #21901.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
mksh R48

Closes #21896.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
transmission 2.82

Closes #21883.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
sonar-runner 2.3

Closes #21905.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
sdl2: fix HEAD

Closes #21886.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
unpack: extract usage
unpack: don't call realpath on potentially non-existent directory
unpack: don't attempt to chdir into regular files
audit: show real name for aliases
go: add option for building without cgo

Closes #20960.

Signed-off-by: Adam Vandenberg <flangy@gmail.com>
go: use buildpath
terminal-notifier: style nits
add ubuntu package search