mlton is a binary-only formula that only works when installed
to /usr/local. Moving it, and things that depend on it to the
boneyard.

Closes Homebrew/homebrew#21780.

Closes Homebrew/homebrew#27346.

Turns out that this doesn't really work at all. `brew install` _never_
reuses options in the first place, and using this option with `brew
upgrade` results in some nasty corner cases in passing options to
dependencies.

When only_deps is true, this method is never called.

Previously, with nested arrays, the Symbol#to_proc would iterate over
the first item in the nested array instead of the array itself, e.g.:

[[1,2], [3,4]].map(&:first) #=>
	NoMethodError: undefined method `first' for 1:Fixnum

Closes Homebrew/homebrew#27322.

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

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

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

With that option iterate only over `Formula.installed`, otherwise
iterate over `Formula`. This is faster than iterating over all the
formulae and checking if it's installed.

Fixes Homebrew/homebrew#27259.
Closes Homebrew/homebrew#27295.

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

This reverts commit b603c96276cf7fe1417d2355eebc47fb15da0b8c.

Fixes Homebrew/homebrew#27265.

Kerl does not provide git tags, so move to headonly.

Closes Homebrew/homebrew#26307.

Fixes Homebrew/homebrew#27245.