Expand '~' in path to extensions.

doc/hgrc.5.txt

@@ -165,6 +165,14 b' extensions::'
   the path to the ".py" file (including the file name extension) that
   defines the extension.
 
+  Example for ~/.hgrc:
+
+    [extensions]
+    # (the mq extension will get loaded from mercurial's path)
+    hgext.mq =
+    # (this extension will get loaded from the file specified)
+    myfeature = ~/.hgext/myfeature.py
+
 hooks::
   Commands or Python functions that get automatically executed by
   various actions such as starting or finishing a commit. Multiple

mercurial/ui.py

@@ -142,7 +142,10 b' class ui(object):'
                 yield parent
 
     def extensions(self):
-        return self.configitems("extensions")
+        ret = self.configitems("extensions")
+        for i, (k, v) in enumerate(ret):
+            if v: ret[i] = (k, os.path.expanduser(v))
+        return ret
 
     def hgignorefiles(self):
         result = []