Fixes Homebrew/homebrew#136

Turns out $?.to_i is a 16bit int with some bit flags in the first byte.

-fomit-frame-pointer is included for any optimisation level above O2 (including Os)

Setting MACOS_DEPLOYMENT_TARGET is unecessary if you are just setting it the same as the OS X you are running.

Makes a big difference on OS X, you can still use the GUI and that.

This is what we did for gcc_4_2 after all.

This means our include directory is prioritised above all -I but after all other system directories. This is how it should be.

Also helps fix Homebrew/homebrew#113.

Thus mv, rm etc, functions are almost as handy as pure shell scripting, without issues related to spaces in filenames.

Some gems and libraries seem to change the order.

Where brew info will show the next-level-down dependencies, brew deps
will show all of the formulae that a given formula depends on.

* brew install will find an aliased formula
* aliases are searched against
* warn when creating a new formula that has an existing alias.

If Subversion has an alias "svn", then warn when the user tries to
create a new formula "svn". The formula can still be created, though
the user should make sure it's not a duplicate of the existing
aliased one.

Subversion and Objective-Caml formulas get some alises here, so we have
something to test against.

'uses' shows the formulas that depend on a formula given on the
command-line.

These methods could be static on Formula, but splitting them out makes
it clear to formular authors that these functions don't have anything
to do with writing new formulas.

The code in Keg.self.for path uses "path = path.parent.realpath" to walk
up subfolders looking for a Keg.

Because 'realpath' is in there, and the path is checked against
HOMEBREW_CELLAR, which  may be a symlink, we need to do realpath-to-realpath
comparisons in Keg. Otherwise, we will hit equivalent but symlinked folders,
not see that they are the same, and walk all the way up to / and then
error out.

If an exception is thrown while parsing the formula file before the install.rb at_exit then it will be in $!. Marshal it back to the parent brew process.

Rather than showing a backtrace that says "couldn't find command blah". Admittedly it's possible that the error will be something else, but unlikely. And this is neater.

Ideally we'd push the bt through an error pipe like we do with install.rb. And I guess we'll do this eventually.

The reason we rescue this exception at all is because otherwise our general purpose Exception handler catches it.

Ideally we could do a get request and fill in the issue form at GitHub. Presumably though, we'd only do this if the user typed brew report or somesuch.

Someone should get that implemented!

It's a great feature but it seems to conflict with our new system() replacement. Clearly the bug is still in our system() but what exactly it is is not clear and this bug sucks.

See Homebrew/homebrew#124