Ensure Poppler's minimal version

We're using methods that aren't available in Poppler
below 0.46, so we're checking for this upon import.

This commit is based on ideas from @LogicalDash ♥

libmat2/pdf.py

@@ -7,6 +7,7 @@ import re
 import logging
 import tempfile
 import io
+from distutils.version import LooseVersion
 
 import cairo
 import gi
@@ -17,6 +18,11 @@ from . import abstract
 
 logging.basicConfig(level=logging.DEBUG)
 
+poppler_version = Poppler.get_version()
+if LooseVersion(poppler_version) < LooseVersion('0.46'):
+    raise ValueError("MAT2 needs at least Poppler version 0.46 to work. \
+The installed version is %s." % poppler_version)
+
 
 class PDFParser(abstract.AbstractParser):
     mimetypes = {'application/pdf', }