extensions: extract partial application into a bind() function

We use partial function application for wrapping existing Mercurial functions,
and it's implemented separately each time.  This patch extracts the partial
application into a new bind() function that can be used on its own by extensions
when appropriate.

In particular, the evolve extension needs to wrap functions in the various
bundle2 processing dictionaries, which the pre-existing methods don't support.

mercurial/extensions.py

@@ -152,6 +152,18 b' def afterloaded(extension, callback):'
     else:
         _aftercallbacks.setdefault(extension, []).append(callback)
 
+def bind(func, *args):
+    '''Partial function application
+
+      Returns a new function that is the partial application of args and kwargs
+      to func.  For example,
+
+          f(1, 2, bar=3) === bind(f, 1)(2, bar=3)'''
+    assert callable(func)
+    def closure(*a, **kw):
+        return func(*(args + a), **kw)
+    return closure
+
 def wrapcommand(table, command, wrapper, synopsis=None, docstring=None):
     '''Wrap the command named `command' in table
 
@@ -189,9 +201,7 b' def wrapcommand(table, command, wrapper,'
             break
 
     origfn = entry[0]
-    def wrap(*args, **kwargs):
-        return util.checksignature(wrapper)(
-            util.checksignature(origfn), *args, **kwargs)
+    wrap = bind(util.checksignature(wrapper), util.checksignature(origfn))
 
     wrap.__module__ = getattr(origfn, '__module__')
 
@@ -241,12 +251,10 b' def wrapfunction(container, funcname, wr'
     subclass trick.
     '''
     assert callable(wrapper)
-    def wrap(*args, **kwargs):
-        return wrapper(origfn, *args, **kwargs)
 
     origfn = getattr(container, funcname)
     assert callable(origfn)
-    setattr(container, funcname, wrap)
+    setattr(container, funcname, bind(wrapper, origfn))
     return origfn
 
 def _disabledpaths(strip_init=False):