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', }

mat2

@@ -8,7 +8,11 @@ import mimetypes
 import argparse
 import multiprocessing
 
-from libmat2 import parser_factory, unsupported_extensions
+try:
+    from libmat2 import parser_factory, unsupported_extensions
+except ValueError as e:
+    print(e)
+    sys.exit(1)
 
 __version__ = '0.1.2'