Wrap config snapshot functions

These allow complex reads to come from the same version of the config.

pygit2/config.py

@@ -223,6 +223,19 @@ class Config(object):
         err = C.git_config_add_file_ondisk(self._config, to_str(path), level, force)
         check_error(err)
 
+    def snapshot(self):
+        """Create a snapshot from this Config object
+
+        This means that looking up multiple values will use the same version
+        of the configuration files
+        """
+
+        ccfg = ffi.new('git_config **')
+        err = C.git_config_snapshot(cfg, self._config)
+        check_error(err)
+
+        return Config.from_c(self._repo, ccfg[0])
+
     #
     # Methods to parse a string according to the git-config rules
     #

pygit2/decl.h

@@ -255,6 +255,7 @@ typedef struct {
 } git_config_entry;
 
 int git_repository_config(git_config **out, git_repository *repo);
+int git_repository_config_snapshot(git_config **out, git_repository *repo);
 void git_config_free(git_config *cfg);
 
 int git_config_get_string(const char **out, const git_config *cfg, const char *name);
@@ -279,6 +280,7 @@ int git_config_multivar_iterator_new(git_config_iterator **out, const git_config
 int git_config_set_multivar(git_config *cfg, const char *name, const char *regexp, const char *value);
 
 int git_config_new(git_config **out);
+int git_config_snapshot(git_config **out, git_config *config);
 int git_config_open_ondisk(git_config **out, const char *path);
 int git_config_find_system(git_buf *out);
 int git_config_find_global(git_buf *out);

pygit2/repository.py

@@ -128,6 +128,19 @@ class Repository(_Repository):
 
         return Config.from_c(self, cconfig[0])
 
+    @property
+    def config_snapshot(self):
+        """A snapshot for this repositiory's configuration
+
+        This allows reads over multiple values to use the same version
+        of the configuration files"""
+
+        cconfig = ffi.new('git_config **')
+        err = C.git_repository_config_snapshot(cconfig, self._repo)
+        check_error(err)
+
+        return Config.from_c(self, cconfig[0])
+
     #
     # References
     #