Different regex for user/tap/formula and user/tap.

Closes Homebrew/homebrew#23430.

Library/Homebrew/cmd/install.rb

@@ -16,7 +16,7 @@ module Homebrew extend self
         msg = blacklisted? name
         raise "No available formula for #{name}\n#{msg}" if msg
       end
-      if not File.exist? name and name =~ HOMEBREW_TAP_REGEX then
+      if not File.exist? name and name =~ HOMEBREW_TAP_FORMULA_REGEX then
         require 'cmd/tap'
         begin
           install_tap $1, $2

Library/Homebrew/cmd/search.rb

@@ -4,6 +4,12 @@ require 'utils'
 require 'utils/json'
 
 module Homebrew extend self
+
+  # A regular expession to capture the username (one or more char but no `/`,
+  # which has to be escaped like `\/`), repository, followed by an optional `/`
+  # and an optional query.
+  TAP_QUERY_REGEX = /^([^\/]+)\/([^\/]+)\/?(.+)?$/
+
   def search
     if ARGV.include? '--macports'
       exec_browser "http://www.macports.org/ports.php?by=name&substr=#{ARGV.next}"
@@ -19,7 +25,7 @@ module Homebrew extend self
       exec_browser "http://packages.ubuntu.com/search?keywords=#{ARGV.next}&searchon=names&suite=all&section=all"
     elsif (query = ARGV.first).nil?
       puts_columns Formula.names
-    elsif ARGV.first =~ HOMEBREW_TAP_REGEX
+    elsif ARGV.first =~ TAP_QUERY_REGEX
       # So look for user/repo/query or list all formulae by the tap
       # we downcase to avoid case-insensitive filesystem issues.
       user, repo, query = $1.downcase, $2.downcase, $3

Library/Homebrew/exceptions.rb

@@ -44,7 +44,7 @@ class FormulaUnavailableError < RuntimeError
   end
 
   def to_s
-    if name =~ HOMEBREW_TAP_REGEX then <<-EOS.undent
+    if name =~ HOMEBREW_TAP_FORMULA_REGEX then <<-EOS.undent
       No available formula for #$3 #{dependent_s}
       Please tap it and then try again: brew tap #$1/#$2
       EOS

Library/Homebrew/global.rb

@@ -83,10 +83,7 @@ HOMEBREW_USER_AGENT = "Homebrew #{HOMEBREW_VERSION} (Ruby #{RUBY_VERSION}-#{RUBY
 
 HOMEBREW_CURL_ARGS = '-f#LA'
 
-# A regular expession to capture the username (one or more char but no `/`,
-# which has to be escaped like `\/`), repository, followed by an optional `/`
-# and an optional query.
-HOMEBREW_TAP_REGEX = /^([^\/]+)\/([^\/]+)\/?(.+)?$/
+HOMEBREW_TAP_FORMULA_REGEX = %r{(\w+)/(\w+)/([^/]+)}
 
 module Homebrew extend self
   include FileUtils