discards no constrains constrains

lib/pluginmanager/gemfile.rb

@@ -107,8 +107,8 @@ def add_gem(_gem)
     # update existing or add new
     def update_gem(_gem)
       if old = find_gem(_gem.name)
-        # always overwrite requirements
-        old.requirements = _gem.requirements
+        # always overwrite requirements if specified
+        old.requirements = _gem.requirements unless no_constrains?(_gem.requirements)
         # but merge options
         old.options = old.options.merge(_gem.options)
       else
@@ -139,8 +139,19 @@ def remove_gem(name)
     def copy
       Marshal.load(Marshal.dump(self))
     end
+
     private
 
+    def no_constrains?(requirements)
+      return true if requirements.nil? || requirements.empty?
+
+      # check for the dummy ">= 0" version constrain or any variations thereof
+      # which is in fact a "no constrain" constrain which we should discard
+      return true if requirements.size == 1 && requirements.first.to_s.gsub(/\s+/, "") == ">=0"
+
+      false
+    end
+
     def sources_to_s
       return "" if @sources.empty?
       @sources.map{|source| "source #{source.inspect}"}.join("\n")