Introduced posibility to change number of sample points for pvt.

Did change the PVTW calculation so derivatives are exact.
Extended the test functions for pvt and relperm

opm/core/fluid/BlackoilPropertiesFromDeck.cpp

@@ -39,7 +39,8 @@ namespace Opm
                                                            const parameter::ParameterGroup& param)
     {
         rock_.init(deck, grid);
-        pvt_.init(deck);
+        int samples = param.getDefault("dead_tab_size", 1025);
+        pvt_.init(deck, samples);
         satprops_.init(deck, grid, param);
 
         if (pvt_.numPhases() != satprops_.numPhases()) {

opm/core/fluid/blackoil/BlackoilPvtProperties.hpp

@@ -47,7 +47,7 @@ namespace Opm
         BlackoilPvtProperties();
 
         /// Initialize from deck.
-	void init(const EclipseGridParser& deck);
+    void init(const EclipseGridParser& deck,const int samples = 16);
 
         /// Number of active phases.
         int numPhases() const;