Bump SO major number as we have introduced API breakage.

Use version number as 0.5-dev, instead of 0.5.

Make.inc

@@ -3,8 +3,8 @@
 OS := $(shell uname)
 # Do not forget to bump SOMINOR when changing VERSION,
 # and SOMAJOR when breaking ABI in a backward-incompatible way
-VERSION = 0.5
-SOMAJOR = 1
+VERSION = 0.5-dev
+SOMAJOR = 2
 SOMINOR = 1
 DESTDIR =
 prefix = /usr/local