Strictly require Varnish 5.1.x.

README.rst

@@ -903,9 +903,8 @@ Example::
 REQUIREMENTS
 ============
 
-The VMOD requires Varnish since version 5.1.0. See the source
-repository for versions of the VMOD that are compatible with other
-Varnish versions.
+The VMOD requires Varnish version 5.1.x. See the source repository for
+versions of the VMOD that are compatible with other Varnish versions.
 
 It requires the RE2 library, and has been tested against RE2 version
 2017-06-01.

configure.ac

 AC_PREREQ(2.59)
 AC_COPYRIGHT([Copyright (c) 2016 UPLEX - Nils Goroll Systemoptimierung])
-AC_INIT([libvmod-re2], [trunk])
+AC_INIT([libvmod-re2], [v1.3])
 AC_CONFIG_MACRO_DIR([m4])
 m4_ifndef([VARNISH_VMOD_INCLUDES], AC_MSG_ERROR([Need varnish.m4 -- see README.rst]))
 AC_CONFIG_SRCDIR(src/vmod_re2.vcc)
@@ -67,7 +67,7 @@ AS_VAR_IF([$1], [""], [$5], [$4])dnl
 ])# PKG_CHECK_VAR
 ])
 
-PKG_CHECK_MODULES([libvarnishapi], [varnishapi])
+PKG_CHECK_MODULES([libvarnishapi], [varnishapi >= 5.1.0 varnishapi <= 5.1.2])
 PKG_CHECK_VAR([LIBVARNISHAPI_DATAROOTDIR], [varnishapi], [datarootdir])
 PKG_CHECK_VAR([LIBVARNISHAPI_BINDIR], [varnishapi], [bindir])
 PKG_CHECK_VAR([LIBVARNISHAPI_SBINDIR], [varnishapi], [sbindir])

src/vmod_re2.vcc

@@ -771,9 +771,8 @@ Example::
 REQUIREMENTS
 ============
 
-The VMOD requires Varnish since version 5.1.0. See the source
-repository for versions of the VMOD that are compatible with other
-Varnish versions.
+The VMOD requires Varnish version 5.1.x. See the source repository for
+versions of the VMOD that are compatible with other Varnish versions.
 
 It requires the RE2 library, and has been tested against RE2 version
 2017-06-01.