Makefile.defs: version set to 5.4.0-pre0

- start of pre-release phase for 5.4.x series

src/Makefile.defs

@@ -107,7 +107,7 @@ INSTALL_FLAVOUR=$(FLAVOUR)
 VERSION = 5
 PATCHLEVEL = 4
 SUBLEVEL =  0
-EXTRAVERSION = -dev6
+EXTRAVERSION = -pre0
 
 # memory manager switcher
 # 0 - f_malloc (fast malloc)