Bump soname for v0.7.

We have added new public interfaces, but are still backward
compatible with clients built against older releases.

configure.ac

@@ -33,9 +33,9 @@ dnl - interfaces added/removed/changed -> increment CURRENT, REVISION = 0
 dnl - interfaces added -> increment AGE
 dnl - interfaces removed -> AGE = 0
 
-OP_LT_CURRENT=3
-OP_LT_REVISION=1
-OP_LT_AGE=3
+OP_LT_CURRENT=4
+OP_LT_REVISION=0
+OP_LT_AGE=4
 
 AC_SUBST(OP_LT_CURRENT)
 AC_SUBST(OP_LT_REVISION)