Rename git_branch_lookup to simply branch_lookup.

As recommended by @jdavid at libgit2#221.

pygit2/repository.py

@@ -99,13 +99,13 @@ def __init__(self, repository, branch_type):
             self._branch_type = branch_type
 
         def __getitem__(self, key):
-            value = self._repository.git_branch_lookup(key, self._branch_type)
+            value = self._repository.branch_lookup(key, self._branch_type)
             if value is None:
                 raise KeyError(key)
             return value
 
         def __contains__(self, key):
-            return self._repository.git_branch_lookup(key, self._branch_type) is not None
+            return self._repository.branch_lookup(key, self._branch_type) is not None
 
     @property
     def branches(self):

src/repository.c

@@ -268,13 +268,13 @@ Repository_git_object_lookup_prefix(Repository *self, PyObject *key)
 }
 
 
-PyDoc_STRVAR(Repository_git_branch_lookup__doc__,
-  "git_branch_lookup(branch_name, [branch_type]) -> Object\n"
+PyDoc_STRVAR(Repository_branch_lookup__doc__,
+  "branch_lookup(branch_name, [branch_type]) -> Object\n"
   "\n"
   "Returns the Git reference for the given branch name (local or remote).");
 
 PyObject *
-Repository_git_branch_lookup(Repository *self, PyObject *args)
+Repository_branch_lookup(Repository *self, PyObject *args)
 {
     git_reference *c_reference;
     const char *c_name;
@@ -1360,7 +1360,7 @@ PyMethodDef Repository_methods[] = {
     METHOD(Repository, create_note, METH_VARARGS),
     METHOD(Repository, lookup_note, METH_VARARGS),
     METHOD(Repository, git_object_lookup_prefix, METH_O),
-    METHOD(Repository, git_branch_lookup, METH_VARARGS),
+    METHOD(Repository, branch_lookup, METH_VARARGS),
     METHOD(Repository, listall_branches, METH_VARARGS),
     METHOD(Repository, create_branch, METH_VARARGS),
     {NULL}