[meld] bin/meld: Check for pycairo dependency (#313)

[Kai Willadsen <kaiw src gnome org>]

commit f464ed627ca684150f18f00bcc9759378c081889
Author: Kai Willadsen <kai willadsen gmail com>
Date:   Mon Apr 22 08:27:52 2019 +1000

    bin/meld: Check for pycairo dependency (#313)
    
    This is distinct from the GI bindings, because we use the non-GI
    `cairo.Surface.create_similar()`.

 bin/meld | 7 +++++++
 1 file changed, 7 insertions(+)
---
diff --git a/bin/meld b/bin/meld
index 80cea756..6a8ff9eb 100755
--- a/bin/meld
+++ b/bin/meld
@@ -181,6 +181,7 @@ def show_error_and_exit(error_text):
 
 def check_requirements():
 
+    cairo_requirement = (1, 15)
     gtk_requirement = (3, 20)
     glib_requirement = (2, 48)
     gtksourceview_requirement = (3, 20, 0)
@@ -221,6 +222,12 @@ def check_requirements():
     except (ImportError, AssertionError, ValueError) as e:
         missing_reqs("GtkSourceView 3", gtksourceview_requirement, e)
 
+    try:
+        import cairo
+        assert cairo.version_info >= cairo_requirement
+    except (ImportError, AssertionError) as e:
+        missing_reqs("cairo", cairo_requirement, e)
+
 
 def setup_resources():
     from gi.repository import Gio