Make the underlying git_revwalk object accessible

Author: tiennou

ObjectiveGit/GTEnumerator.h

@@ -64,6 +64,9 @@ NS_ASSUME_NONNULL_BEGIN
 
 - (instancetype)init NS_UNAVAILABLE;
 
+/// The underlying `git_revwalk` from libgit2.
+- (git_revwalk *)git_revwalk __attribute__((objc_returns_inner_pointer));
+
 /// Initializes the receiver to enumerate the commits in the given repository. Designated initializer.
 ///
 /// repo  - The repository to enumerate the commits of. This must not be nil.

ObjectiveGit/GTEnumerator.m

@@ -53,6 +53,10 @@ - (instancetype)init {
 	return nil;
 }
 
+- (git_revwalk *)git_revwalk {
+	return self.walk;
+}
+
 - (instancetype)initWithRepository:(GTRepository *)repo error:(NSError **)error {
 	NSParameterAssert(repo != nil);