Increase libvarnishapi libtool revision number.

This number was last changed between Varnish 1.0 and Varnish 2.0.

As far as I can read from the commits, we haven't actually removed
any interfaces in any released Varnish versions, so a revision bump
should be all that is needed.

Another possibility is to stop using -version-info and just roll
our own scheme with -release, but I don't want to go down that route
just before 4.1.0.

lib/libvarnishapi/Makefile.am

@@ -9,7 +9,7 @@ AM_CPPFLAGS = \
 
 lib_LTLIBRARIES = libvarnishapi.la
 
-libvarnishapi_la_LDFLAGS = $(AM_LDFLAGS) -version-info 1:0:0
+libvarnishapi_la_LDFLAGS = $(AM_LDFLAGS) -version-info 1:4:0
 
 libvarnishapi_la_SOURCES = \
 	vsm_api.h \