Make python-beaker an optional dependency

Mako can work fine without beaker.
Beaker is the preferred caching backend, so the Fedora
package should pull it in by default, but it should also
be possible to disable it in more restricted environments.

Notes:

* Beaker is not mentioned as a dependency in setup.py.

* Technically the optional dependency works by having
  imports like the following (from mako/ext/beaker_cache.py):

      try:
          from beaker import cache as beaker_cache
      except:
          has_beaker = False
      else:
          has_beaker = True

python-mako.spec

@@ -6,7 +6,7 @@
 
 Name: python-mako
 Version: 1.0.6
-Release: 8%{?dist}
+Release: 9%{?dist}
 BuildArch: noarch
 
 # Mostly MIT, but _ast_util.py is Python licensed.
@@ -50,7 +50,10 @@ calling and scoping semantics.
 %package -n python2-mako
 Summary: %summary
 Requires: python2-markupsafe
-Requires: python2-beaker
+
+# Beaker is the preferred caching backend, but is not strictly necessary
+Recommends: python2-beaker
+
 %{?python_provide:%python_provide python2-mako}
 
 %description -n python2-mako %_description
@@ -78,9 +81,11 @@ This package contains documentation in text and HTML formats.
 %package -n python3-mako
 Summary: Mako template library for Python 3
 Group: Development/Languages
-Requires: python3-beaker
 Requires: python3-markupsafe
 
+# Beaker is the preferred caching backend, but is not strictly necessary
+Recommends: python3-beaker
+
 %description -n python3-mako
 Mako is a template library written in Python. It provides a familiar, non-XML
 syntax which compiles into Python modules for maximum performance. Mako's
@@ -158,6 +163,9 @@ popd
 
 
 %changelog
+* Wed Mar 28 2018 Petr Viktorin <pviktori@redhat.com> - 1.0.6-9
+- Make python-beaker an optional dependency
+
 * Mon Feb 12 2018 Iryna Shcherbina <ishcherb@redhat.com> - 1.0.6-8
 - Update Python 2 dependency declarations to new packaging standards
   (See https://fedoraproject.org/wiki/FinalizingFedoraSwitchtoPython3)