Using popen here breaks brew install -v due to the way
the error pipe is passed around during install.

Moved snow_leopard_64? to compatibility and replaced it with
a function MacOS.prefer_64_bit?. This method is in a better
place and has a better name once Lion comes out.

Fixes Homebrew/homebrew#4710

Closes Homebrew/homebrew#4693.

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

System duplicates can now provide more information about why
they are included in Homebrew.

Fixes Homebrew/homebrew#4683

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

If version cannot be determined, then instruct the user to add one.

Because we should always be able to help. And I've checked, it works fine.

Be more useful by being more concise. I referenced dozens of other mature commands’ usage to figure out what to do here.

Also separated out the help into its own command for consistency.

Because since 0.8 we do the opposite, ie. download by default.

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

This provides a uniform way for formulae to indicate a Fortran compiler
is required.

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

Prefer a shallow clone for builds from git repos, as we don't need all
the historical stuff.

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