Makefile.defs: version set to 5.7.0-dev0

- master branch is open for new features to be part of future release
  series 5.7.x

src/Makefile.defs

@@ -105,9 +105,9 @@ INSTALL_FLAVOUR=$(FLAVOUR)
 
 # version number
 VERSION = 5
-PATCHLEVEL = 6
+PATCHLEVEL = 7
 SUBLEVEL =  0
-EXTRAVERSION = -pre2
+EXTRAVERSION = -dev0
 
 # memory manager switcher
 # 0 - f_malloc (fast malloc)