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.

In order to allow kegs built with the same version but differing formula
revisions to coexist, we must encode the revision as part of the keg's
name. This is necessary to actually perform an upgrade, as we cannot
upgrade a keg in-place, and temporarily moving it pending the result of
the upgrade is error-prone and potentially slow.

To accomplish this, we introduce a new Formula#pkg_version method that
concatenates the active_spec version with the formula revision. An
exception is made for a formula that has no revision: the tag is
omitted. This preserves compatibility with existing installations.

It is useful to be able to prompt upgrades in response to events other
than a version update; for example, when a dependency is updated and its
library version changes, dependents need to be rebuilt to link against
the new library.

Currently we cannot do this automatically, which means a flood of
tickets whenever the library version of a popular library changes.

To address this, we need to track an additional piece of metadata, the
"revision" of the formula, which can be incremented when appropriate to
prompt an upgrade. It can then be reset to zero when the next version
change occurs.