[Version] Updated #to_s and added Version.from_s.

lib/cocoapods/specification.rb

@@ -447,13 +447,7 @@ module Pod
     end
 
     def to_s
-      if !version
-        name
-      elsif version.head?
-        "#{name} (HEAD from #{version})"
-      else
-        "#{name} (#{version})"
-      end
+      version ? "#{name} (#{version})" : name
     end
 
     def inspect

lib/cocoapods/version.rb

-
-
 module Pod
   class Version < Gem::Version
+
+    # @returns A Version described by its #to_s method.
+    #
+    def self.from_s(string)
+      match = string.match(/HEAD from (.*)/)
+      string = match[1] if match
+      vers = Version.new(string)
+      vers.head = true if match
+      vers
+    end
+
     attr_accessor :head
     alias_method :head?, :head
+
+    def to_s
+      head? ? "HEAD from #{super}" : super
+    end
   end
 end