Merge branch 'v2.4' into v2.5

CHANGES/v2.4.md

@@ -208,6 +208,7 @@ For users:
   - Updated NAMD patches to version 2.12 and 2.13. Old patches have been removed.
   - GROMACS patch for gromacs-2018.4.
   - Fixed a bug in CS2BACKBONE when using more than 2 chains
+  - Fixed a threadsafety issue using forces on histograms
 
 For developers:
   - All fixed done in version 2.3.8

src/analysis/Histogram.cpp

@@ -213,6 +213,7 @@ public:
   void prepareForAveraging();
   void performOperations( const bool& from_update );
   void finishAveraging();
+  bool threadSafe() const { return !in_apply; }
   bool isPeriodic() { return false; }
   unsigned getNumberOfDerivatives();
   void turnOnDerivatives();