Provide a gentle nudge to users to check if these dependencies are
definitely required.

This is used to indicate a formula is a version of another formula.
This will be used to provide a consistent interface for older formulae
versions and replaces the use of `conflicts_with`.

Not quite a mass replacement as I've used OS X and Mac OS X where
describing specific older versions and added compatibility methods
for things in the DSL.

But remove some manual `.freeze`s on constants that shouldn't be
constants.

`Formula#keg_only?` could fail if it was invoked on a formula with a
`:provided_until_xcode43` or `:provided_until_xcode5` reason given to
`keg_only`, if neither the Command Line Tools nor Xcode was installed.
Check whether Xcode is installed before querying the Xcode version.

Closes #317.

Closes Homebrew/homebrew#45337.

Signed-off-by: Baptiste Fontaine <batifon@yahoo.fr>

This prevents typos like `bottle :uneeded` or `bottle :disable`

Closes Homebrew/homebrew#45264.

Signed-off-by: Xu Cheng <xucheng@me.com>

Closes Homebrew/homebrew#42460.

Signed-off-by: Dominyk Tiller <dominyktiller@gmail.com>

Closes Homebrew/homebrew#42073.

Signed-off-by: Baptiste Fontaine <batifon@yahoo.fr>

It will cut off the beginning of any interpolated lines.

Fixes Homebrew/homebrew#32259.

Closes Homebrew/homebrew#31951.

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

Closes Homebrew/homebrew#28095.

Closes Homebrew/homebrew#18300.
Closes Homebrew/homebrew#20891.

Closes Homebrew/homebrew#20357.

Closes Homebrew/homebrew#20239.

This is initialized in #initialize.

Reader methods for specific checksum types have been absent from the
Formula class for some time, so there isn't any reason to expose them in
SoftwareSpec, either.

Thus, these methods now only act as setters, and #checksum should be
used to access the constructed Checksum object.

This has two parts:

1. Bottles are temporarily relocated on bottling and tested if that is
sufficient for them to contain no longer reference the prefix or
cellar. If so, they are marked as relocatable.
2. On installation if bottles are marked as relocatable they will be
relocated using install_name_tool to the current prefix and cellar.

Closes Homebrew/homebrew#18374.

These are redefined later for use in the bottle DSL.

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

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

* Remove legacy url syntax.
* Use revision instead of version.

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