* 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

As I understand it (I tested too), signal propogation is handled by the parent Ruby process. However this was working mostly anyway. So I don't fully understand what is going on. However this seems to not hang in Process.wait where it was before for one test case.

It just seems to behave strangely with SIGINT. Eg. SIGINT causes tar to exit, but the SIGINT is ignored by our process. This is not the case when used with curl.

We need a test for this.

Closes Homebrew/homebrew#116

Thus install.rb gets the path to the instantiating brew process rather than whichever is first in the PATH. Not to mention Homebrew doesn't *have* to be in the PATH.

Because it's a global.h constant and that file can be included by other projects.

It's a constant and Dir.getwd can change.