Clarify behavior of brew search without an argument

As documented in the man page, when given no arguments, `brew search`
will list all formulae. This is different than giving an *empty*
argument.

Library/Homebrew/cmd/search.rb

@@ -11,13 +11,14 @@ module Homebrew extend self
       exec_browser "http://pdb.finkproject.org/pdb/browse.php?summary=#{ARGV.next}"
     elsif ARGV.include? '--debian'
       exec_browser "http://packages.debian.org/search?keywords=#{ARGV.next}&searchon=names&suite=all&section=all"
+    elsif (query = ARGV.first).nil?
+      puts_columns Formula.names
     else
-      query = ARGV.first
       rx = query_regexp(query)
       local_results = search_formulae(rx)
       puts_columns(local_results)
 
-      if not query.to_s.empty? and $stdout.tty? and msg = blacklisted?(query)
+      if not query.empty? and $stdout.tty? and msg = blacklisted?(query)
         unless local_results.empty?
           puts
           puts "If you meant #{query.inspect} precisely:"
@@ -26,7 +27,6 @@ module Homebrew extend self
         puts msg
       end
 
-      if query
       tap_results = search_taps(rx)
       puts_columns(tap_results)
       count = local_results.length + tap_results.length
@@ -41,7 +41,6 @@ module Homebrew extend self
       end
     end
   end
-  end
 
   SEARCHABLE_TAPS = [
     %w{josegonzalez php},
@@ -57,7 +56,6 @@ module Homebrew extend self
 
   def query_regexp(query)
     case query
-    when nil then ""
     when %r{^/(.*)/$} then Regexp.new($1)
     else /.*#{Regexp.escape(query)}.*/i
     end
@@ -90,11 +88,8 @@ module Homebrew extend self
   end
 
   def search_formulae rx
-    if rx.to_s.empty?
-      Formula.names
-    else
     aliases = Formula.aliases
-      results = (Formula.names+aliases).grep rx
+    results = (Formula.names+aliases).grep(rx)
 
     # Filter out aliases when the full name was also found
     results.reject do |alias_name|
@@ -104,5 +99,4 @@ module Homebrew extend self
       end
     end
   end
-  end
 end