This allows us to force using the system Ruby on OSX but allow
the development of Homebrew for Linux or Windows to not rely
on OSX paths.

Closes Homebrew/homebrew#17548.

Closes Homebrew/homebrew#17654.

This can cause subtle issues when an exception is marshaled between the
build process and the main Homebrew process, as the marshaled exception
may contain URI objects even when the main Homebrew process has not
loaded the URI library.

Closes Homebrew/homebrew#17642.

Overriding <=> directly is much simpler.

We want to be able to test the raise functionality without
monkey-patching #raise on every object in the system, which is one of
the side effects of loading debrew.rb.

If the debugger's monkey-patched raise was passed an instantiated
exception, the #exception method was called with a potentially nil
argument, causing its instance data to be thrown away. This hides
potentially useful information from the user.

Fix it by allowing instantiated exceptions to be reraised unharmed.

Fixes Homebrew/homebrew#17622.

Closes Homebrew/homebrew#17588.

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

Closes Homebrew/homebrew#17443.

Closes Homebrew/homebrew#17565.

Closes Homebrew/homebrew#11154.

* `CurlDownloadStrategy#_fetch` (and the same methods in its
  subclasses) now fetches the file to a temporary path, and
  `CurlDownloadStrategy#fetch` moves it to the correct location.
* `Homebrew#cleanup` cleans the temporary files `CurlDownloadStrategy`
  creates if they're left in the cache.

Closes Homebrew/homebrew#13953.

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

We do not use X11 to satisfy these deps for consistency reasons,
but we should continue to support the symbols for compatibility.

Remove direct references to checksum types, access them through the
Checksum::TYPES constant instead.

This way it will print when the verification takes place, making it a
bit more obvious which formula it refers to.

Closes Homebrew/homebrew#17518.
Closes Homebrew/homebrew#17511.

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