[meld] Check new pygobject requirement (#340)

[Kai Willadsen <kaiw src gnome org>]

commit dbf9728c044542825deb6a3534f4d098b40b89d1
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Fri Jul 5 08:51:22 2019 +1000

    Check new pygobject requirement (#340)
    
    We need pygobject support for our new GtkTemplate usage, and 3.30 was
    the first stable release that supported this.

 README.md | 2 +-
 bin/meld  | 7 +++++++
 2 files changed, 8 insertions(+), 1 deletion(-)
---
diff --git a/README.md b/README.md
index dfb63fb1..1ae0af55 100644
--- a/README.md
+++ b/README.md
@@ -18,7 +18,7 @@ Requirements
 
 * Python 3.6
 * pycairo (Python3 bindings for cairo without GObject layer)
-* PyGObject 3.20 (Python3 bindings for GObject introspection)
+* PyGObject 3.30 (Python3 bindings for GObject introspection)
 * gsettings-desktop-schemas
 
 And following packages with GObject introspection:
diff --git a/bin/meld b/bin/meld
index ec0e7301..e2ff50e7 100755
--- a/bin/meld
+++ b/bin/meld
@@ -187,6 +187,7 @@ def check_requirements():
     gtk_requirement = (3, 20)
     glib_requirement = (2, 48)
     gtksourceview_requirement = (3, 20, 0)
+    pygobject_requirement = (3, 30, 0)
 
     def missing_reqs(mod, ver, exc=None):
         if isinstance(exc, ImportError):
@@ -198,6 +199,12 @@ def check_requirements():
     if sys.version_info[:2] < meld.conf.PYTHON_REQUIREMENT_TUPLE:
         missing_reqs("Python", meld.conf.PYTHON_REQUIREMENT_TUPLE)
 
+    try:
+        import gi
+        assert gi.version_info >= pygobject_requirement
+    except (ImportError, AssertionError, ValueError) as e:
+        missing_reqs("pygobject", pygobject_requirement, e)
+
     # gtk+ and related imports
     try:
         # FIXME: Extra clause for gi