Add versioning to the plugin architecture

The plugin architecture version can be retrieved by a plugin from the
app mediator by calling the majorVersion and minorVersion methods.

src/MacVim/PlugInImpl.m

@@ -26,6 +26,9 @@
 
 #ifdef MM_ENABLE_PLUGINS
 
+static int MMPlugInArchMajorVersion = 1;
+static int MMPlugInArchMinorVersion = 0;
+
 #import "PlugInImpl.h"
 #import "PlugInGUI.h"
 #import "MMPlugInManager.h"
@@ -219,6 +222,16 @@ MMPlugInAppMediator *sharedAppMediator = nil;
     return nil;
 }
 
+- (int)majorVersion
+{
+    return MMPlugInArchMajorVersion;
+}
+
+- (int)minorVersion
+{
+    return MMPlugInArchMinorVersion;
+}
+
 @end
 
 #endif

src/MacVim/PlugInInterface.h

@@ -39,6 +39,12 @@
 // If there are no instances with the specified class, returns nil.
 - (id)keyPlugInInstanceWithClass:(Class)class;
 
+// Plugin architecture version.  Major versions indicate API incompatibilities.
+// Minor versions may include additions, but nothing that should break current
+// plugins.
+- (int)majorVersion;
+- (int)minorVersion;
+
 @end
 
 @protocol PlugInInstanceMediator