Make build_from_source an explicit installer mode

Library/Homebrew/bottles.rb

@@ -13,7 +13,6 @@ end
 
 def install_bottle? f, options={:warn=>false}
   return true if f.local_bottle_path
-  return false if ARGV.build_from_source?
   return true if ARGV.force_bottle?
   return false unless f.pour_bottle?
   return false unless f.default_build?

Library/Homebrew/cmd/install.rb

@@ -107,6 +107,7 @@ module Homebrew extend self
     fi.ignore_deps = ARGV.ignore_deps? || ARGV.interactive?
     fi.only_deps = ARGV.only_deps?
     fi.build_bottle = ARGV.build_bottle?
+    fi.build_from_source = ARGV.build_from_source?
     fi.prelude
     fi.install
     fi.caveats

Library/Homebrew/cmd/upgrade.rb

@@ -60,6 +60,7 @@ module Homebrew extend self
     installer.options |= Tab.for_formula(f).used_options
     installer.show_header = false
     installer.ignore_deps = false
+    installer.build_from_source = ARGV.build_from_source?
     installer.prelude
 
     oh1 "Upgrading #{f.name}"