merge-homebrew: verify existense of remotes
merge-homebrew: verify existense of remotes

Verify that remotes 'homebrew' and 'origin' exist before proceeding with the Homebrew -> Linuxbrew merge.

Closes Linuxbrew/brew#148.

Signed-off-by: Maxim Belkin <032baa6ccf1d4eaa4536fc4f9b83b9a1f593449a@gmail.com>
hanxue/linuxbrew,Linuxbrew/brew,Linuxbrew/brew,rwhogg/brew,Linuxbrew/brew,rwhogg/brew,Linuxbrew/brew,rwhogg/brew,maxim-belkin/brew,hanxue/linuxbrew,hanxue/linuxbrew,maxim-belkin/brew,maxim-belkin/brew