Replace Homebrew references

Replaces 'Homebrew' references with 'Tigerbrew' in user-visible
messages, and replaces missed references to mxcl/hommebrew.
Document Tiger X11 prefix
xquartz: Set correct last version for Leopard.

Otherwise, `brew doctor` will give a misleading message to update to a
version that really won't work on Leopard.

Signed-off-by: Rogério Brito <rbrito@ime.usp.br>