EAGLE_PLUGIN: read a portion of the design rules and calculate

pad and via sizes from those settings when diameter is not given
in the local object.  Calculation algorithms are inferred from the
UI help of the Eagle program.

For edge connector type of footprints, some copper pads can be on the
back side even within packages.

Flipping of packages to back was not being done correctly, but I think this 
is working now.

There are still remaining issues with text positioning that I am working on.

pcbnew/eagle_plugin.h

@@ -63,6 +63,8 @@ typedef boost::property_tree::ptree     PTREE;
 typedef const PTREE                     CPTREE;
 
 class XPATH;
+struct ERULES;
+
 
 /**
  * Class EAGLE_PLUGIN
@@ -107,6 +109,7 @@ public:
 
 private:
 
+    ERULES*     m_rules;            ///< Eagle design rules.
     XPATH*      m_xpath;            ///< keeps track of what we are working on within
                                     ///< XML document during a Load().
 
@@ -173,6 +176,7 @@ private:
     // all these loadXXX() throw IO_ERROR or ptree_error exceptions:
 
     void loadAllSections( CPTREE& aDocument );
+    void loadDesignRules( CPTREE& aDesignRules );
     void loadLayerDefs( CPTREE& aLayers );
     void loadPlain( CPTREE& aPlain );
     void loadSignals( CPTREE& aSignals );