Add --cache support to hg and bzr.

Library/Homebrew/download_strategy.rb

@@ -253,6 +253,13 @@ private
 end
 
 class MercurialDownloadStrategy <AbstractDownloadStrategy
+  def initialize url, name, version, specs
+    super
+    @clone=HOMEBREW_CACHE+@unique_token
+  end
+
+  def cached_location; @clone; end
+
   def fetch
     raise "You must install mercurial, there are two options:\n\n"+
           "    brew install pip && pip install mercurial\n"+
@@ -261,11 +268,9 @@ class MercurialDownloadStrategy <AbstractDownloadStrategy
           unless system "/usr/bin/which hg"
 
     ohai "Cloning #{@url}"
-    @clone=HOMEBREW_CACHE+@unique_token
-
-    url=@url.sub(%r[^hg://], '')
 
     unless @clone.exist?
+      url=@url.sub(%r[^hg://], '')
       safe_system 'hg', 'clone', url, @clone
     else
       puts "Updating #{@clone}"
@@ -289,16 +294,20 @@ class MercurialDownloadStrategy <AbstractDownloadStrategy
 end
 
 class BazaarDownloadStrategy <AbstractDownloadStrategy
+  def initialize url, name, version, specs
+    super
+    @clone=HOMEBREW_CACHE+@unique_token
+  end
+
+  def cached_location; @clone; end
+
   def fetch
     raise "You must install bazaar first" \
           unless system "/usr/bin/which bzr"
 
     ohai "Cloning #{@url}"
-    @clone=HOMEBREW_CACHE+@unique_token
-
-    url=@url.sub(%r[^bzr://], '')
-
     unless @clone.exist?
+      url=@url.sub(%r[^bzr://], '')
       # 'lightweight' means history-less
       safe_system 'bzr', 'checkout', '--lightweight', url, @clone
     else