Fix for broken hair sim in old files.

Files older than rB37e1285 have broken hair sim due to the (hacky)
velocity "damping" factor, which is not initialized to 1.

source/blender/blenkernel/BKE_blender.h

@@ -42,7 +42,7 @@ extern "C" {
  * and keep comment above the defines.
  * Use STRINGIFY() rather than defining with quotes */
 #define BLENDER_VERSION         271
-#define BLENDER_SUBVERSION      5
+#define BLENDER_SUBVERSION      6
 /* 262 was the last editmesh release but it has compatibility code for bmesh data */
 #define BLENDER_MINVERSION      270
 #define BLENDER_MINSUBVERSION   5

source/blender/blenkernel/intern/particle_system.c

@@ -4012,6 +4012,7 @@ static void do_hair_dynamics(ParticleSimulationData *sim)
 	if (!psys->clmd) {
 		psys->clmd = (ClothModifierData*)modifier_new(eModifierType_Cloth);
 		psys->clmd->sim_parms->goalspring = 0.0f;
+		psys->clmd->sim_parms->vel_damping = 1.0f;
 		psys->clmd->sim_parms->flags |= CLOTH_SIMSETTINGS_FLAG_GOAL|CLOTH_SIMSETTINGS_FLAG_NO_SPRING_COMPRESS;
 		psys->clmd->coll_parms->flags &= ~CLOTH_COLLSETTINGS_FLAG_SELF;
 	}

source/blender/blenloader/intern/versioning_270.c

@@ -35,6 +35,7 @@
 #define DNA_DEPRECATED_ALLOW
 
 #include "DNA_brush_types.h"
+#include "DNA_cloth_types.h"
 #include "DNA_constraint_types.h"
 #include "DNA_sdna_types.h"
 #include "DNA_space_types.h"
@@ -42,6 +43,7 @@
 #include "DNA_object_types.h"
 #include "DNA_mesh_types.h"
 #include "DNA_modifier_types.h"
+#include "DNA_particle_types.h"
 #include "DNA_linestyle_types.h"
 #include "DNA_actuator_types.h"
 
@@ -356,4 +358,19 @@ void blo_do_versions_270(FileData *fd, Library *UNUSED(lib), Main *main)
 			scene->r.preview_start_resolution = 64;
 		}
 	}
+
+	if (!MAIN_VERSION_ATLEAST(main, 271, 6)) {
+		Object *ob;
+		for (ob = main->object.first; ob; ob = ob->id.next) {
+			ModifierData *md;
+
+			for (md = ob->modifiers.first; md; md = md->next) {
+				if (md->type == eModifierType_ParticleSystem) {
+					ParticleSystemModifierData *pmd = (ParticleSystemModifierData*) md;
+					if (pmd->psys && pmd->psys->clmd)
+						pmd->psys->clmd->sim_parms->vel_damping = 1.0f;
+				}
+			}
+		}
+	}
 }