Add a sanity check for the python2 installation.

requirements-python2.txt

@@ -0,0 +1,2 @@
+numpy>=1.10
+typing

sanity-check.py

@@ -0,0 +1,32 @@
+import os
+import re
+import shutil
+import subprocess
+
+
+class GimpInstallationException(Exception):
+    pass
+
+
+if __name__ == '__main__':
+    python = shutil.which('python2')
+    if python is None:
+        raise GimpInstallationException('Could not find a python2 installation.')
+    proc = subprocess.Popen(
+        [python],
+        stdin=subprocess.PIPE,
+        stdout=subprocess.PIPE,
+        stderr=subprocess.PIPE,
+    )
+
+    requirements = open(os.path.join(os.path.dirname(__file__), 'requirements-python2.txt'), 'r').readlines()
+    imports = list(map(lambda r: re.split('[<=>\\s]', r)[0], filter(lambda x: x != '\n', requirements)))
+    import_statements = list(map(lambda r: 'import ' + r, imports))
+    stdout, stderr = proc.communicate(
+        '\n'.join(import_statements).encode(),
+        timeout=5
+    )
+    if stderr.decode() != '':
+        raise GimpInstallationException(
+            'At least one of the following packages is missing in the python2 installation: ' + ', '.join(imports)
+        )