add fully qualified name for core formulae

Library/Homebrew/cmd/install.rb

@@ -14,8 +14,8 @@ module Homebrew
     end
 
     ARGV.named.each do |name|
-      if !File.exist?(name) && (name =~ HOMEBREW_TAP_FORMULA_REGEX \
-                                || name =~ HOMEBREW_CASK_TAP_FORMULA_REGEX)
+      if !File.exist?(name) && (name !~ HOMEBREW_CORE_FORMULA_REGEX) \
+              && (name =~ HOMEBREW_TAP_FORMULA_REGEX || name =~ HOMEBREW_CASK_TAP_FORMULA_REGEX)
         install_tap $1, $2
       end
     end unless ARGV.force?

Library/Homebrew/formulary.rb

@@ -211,6 +211,8 @@ class Formulary
       return FromUrlLoader.new(ref)
     when Pathname::BOTTLE_EXTNAME_RX
       return BottleLoader.new(ref)
+    when HOMEBREW_CORE_FORMULA_REGEX
+      return FormulaLoader.new($1, core_path($1))
     when HOMEBREW_TAP_FORMULA_REGEX
       return TapLoader.new(ref)
     end

Library/Homebrew/tap_constants.rb

@@ -2,6 +2,8 @@
 HOMEBREW_TAP_ARGS_REGEX = %r{^([\w-]+)/(homebrew-)?([\w-]+)$}
 # match taps' formulae, e.g. someuser/sometap/someformula
 HOMEBREW_TAP_FORMULA_REGEX = %r{^([\w-]+)/([\w-]+)/([\w+-.]+)$}
+# match core's formulae, e.g. homebrew/homebrew/someformula
+HOMEBREW_CORE_FORMULA_REGEX = %r{^homebrew/homebrew/([\w+-.]+)$}i
 # match taps' directory paths, e.g. HOMEBREW_LIBRARY/Taps/someuser/sometap
 HOMEBREW_TAP_DIR_REGEX = %r{#{Regexp.escape(HOMEBREW_LIBRARY.to_s)}/Taps/([\w-]+)/([\w-]+)}
 # match taps' formula paths, e.g. HOMEBREW_LIBRARY/Taps/someuser/sometap/someformula