Closes Homebrew/homebrew#33056.

This reverts commit 988601624568a951d86bd00cf441d18681b4b500.

Closes Homebrew/homebrew#33056.

Fixes Homebrew/homebrew#32410.

Fixes Homebrew/homebrew#30472.

Fixes Homebrew/homebrew#27554.

References Homebrew/homebrew#23263.
Closes Homebrew/homebrew#27445.

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.

Only limited debugging functionality is available to things that involve
the Readline formula, but it is better than crashing outright.

c.f. Homebrew/homebrew#15776.

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

A new feature for easing the pain of working with complex formulas, or
formulas for large packages. When running brew in debug mode (-d), if an
exception propagates outside the formula's install method, you now get a menu
which lets you return to the point where the exception was raised and perfom
several useful actions, such as:
- printing a backtrace
- entering IRB to examine the context and test ruby code
- entering the debugger (if ruby-debug is available)
- entering a shell
- ignoring the exception or proceeding with the raise as normal

Signed-off-by: Max Howell <mxcl@me.com>

* Fixed conflict in build.rb.
* Removed old debug handling in Formula.brew.

Closes Homebrew/homebrew#10435.