Use package version to identify interface in soname.

Index: netgen-4.9.12/nglib/Makefile.am
===================================================================
--- netgen-4.9.12.orig/nglib/Makefile.am	2010-03-29 16:55:06.000000000 -0400
+++ netgen-4.9.12/nglib/Makefile.am	2010-03-29 16:55:13.000000000 -0400
@@ -19,7 +19,7 @@
 	$(top_builddir)/libsrc/general/libgeneral.la \
 	$(OCCLIBS) $(MPI_LIBS)
 
-libnglib_la_LDFLAGS = -avoid-version
+libnglib_la_LDFLAGS = -release $(PACKAGE_VERSION)
 #  -rdynamic