Update VCS caches when installing

I held off on this as I wasn't sure it made sense. Eg. if you install you'd expect it to install the same version as before? But with HEAD formula you always want the newest, that's the point. Otherwise it should be tagged/revisioned.

Library/Homebrew/download_strategy.rb

@@ -135,8 +135,8 @@ class SubversionDownloadStrategy <AbstractDownloadStrategy
     unless @co.exist?
       quiet_safe_system svn, 'checkout', @url, @co
     else
-      # TODO svn up?
-      puts "Repository already checked out"
+      puts "Updating #{@co}"
+      quiet_safe_system svn, 'up', @co
     end
   end
 
@@ -162,8 +162,8 @@ class GitDownloadStrategy <AbstractDownloadStrategy
     unless @clone.exist?
       quiet_safe_system 'git', 'clone', @url, @clone
     else
-      # TODO git pull?
-      puts "Repository already cloned to #{@clone}"
+      puts "Updating #{@clone}"
+      Dir.chdir(@clone) { quiet_safe_system 'git', 'fetch', @url }
     end
   end
 
@@ -202,8 +202,9 @@ class CVSDownloadStrategy <AbstractDownloadStrategy
         safe_system '/usr/bin/cvs', '-d', url, 'checkout', '-d', @unique_token, mod
       end
     else
-      # TODO cvs up?
-      puts "Repository already checked out"
+      d = HOMEBREW_CACHE+@unique_token
+      puts "Updating #{d}"
+      Dir.chdir(d) { safe_system '/usr/bin/cvs', 'up' }
     end
   end
 
@@ -242,12 +243,10 @@ class MercurialDownloadStrategy <AbstractDownloadStrategy
     url=@url.sub(%r[^hg://], '')
 
     unless @clone.exist?
-      checkout_args = []
-      checkout_args << url << @clone
-      safe_system 'hg', 'clone', *checkout_args
+      safe_system 'hg', 'clone', url, @clone
     else
-      # TODO hg pull?
-      puts "Repository already cloned"
+      puts "Updating #{@clone}"
+      Dir.chdir(@clone) { safe_system 'hg', 'update' }
     end
   end