Some prefer to install with `--user` into their
home. For example to avoid `sudo` with system's
python. Now Homebrew can use those modules to
satisfy a python dependency on a certain module.

For example python and python3 both provide a
`Python.framework` and OS X Frameworks are made to
deal with this by putting them into `Versions` and
linking the default one as `Current`. However, brew
did not respect this and cleaned out stuff making
neither of the two versions work because `Current`
is replaced by an empty directory.

This commit fixes that. However, still one of the
two `Python.frameworks` has to remove it's
`Current` and `Headers` links, because brew cannot
decide alone which one is the "default" and allowed
to set the `Current` link.

A similar situation might apply to Qt 4 vs. 5..

* Fixes Homebrew/homebrew#20572 by tweaking the logic that decides
  which python is used by the `python` object
  inside a formula. There was a bug when on 10.6
  there is no Python 2.7 but a :recommended
  Python was still treated as being available.

* Use the user's PATH when looking for an external
  Python. Until now only brewed or OS X system's
  python have been found by `depends_on :python`.

  But now we support any Python in PATH (e.g.
  pyenv's python).

* Further, instead of handling python modules
  and import tests in LanguageModuleDependency,
  these are now handled by:

        depends_on :python => 'numpy'  # for example

  The old style

        depends_on 'numpy' => :python

  is still supported and is only an alias
  for the newer style (only for :python, the
  other languages are not altered by this commit).

  The reasoning is that if a formula requires
  a python module, it basically also needs
  python itself - and further that specific
  version of python has to provide the module.
  So the `PythonInstalled` is the natural place
  to check for the availability of a python
  module.

  Using a python module and other tags like
  :optional or :recommended is done like so:

        depends_on :python => [:optional, 'numpy']

  Specifying another PyPi (Python Package index)
  name than the module import name is seldom used
  but supported, too:

         depends_on :python => ['enchant'=>'pyenchant']

  A last note: For clarity, you can define
  multiple depends_on statements with different
  modules to be importable.`

CLT-only builds are still broken and need to be fixed at some point.

Closes Homebrew/homebrew#20524.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Closes Homebrew/homebrew#19998.

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

This command loads all formulae and dumps an HTML profile report to
stdout. So e.g. `brew profile >/tmp/report.html`

Exposing this as "to_a" was a mistake, versions are not arrays and it
causes incorrect behavior when splatted or using Kernel#Array(). Use the
more correct name "tokens" instead.

Closes Homebrew/homebrew#20507.

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

Closes Homebrew/homebrew#20445.

Fixes Homebrew/homebrew#20417.
Closes Homebrew/homebrew#20474.

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

Pinned formulae which were pinned at a previous version but then upgraded
would not be listed by `brew list --pinned`. This is due to the good old
"File.exist? thinks broken symlinks don't exist" gotcha, so the test in
the select block in list_pinned has been changed to check if the pin file
exists _or_ is a symlink.

Closes Homebrew/homebrew#20423.

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

Also complete --devel and the formula's install options.