merge: Return non-const git_repository from git_merge_driver_source_repo accessor.

include/git2/sys/merge.h

@@ -41,7 +41,7 @@ GIT_EXTERN(git_merge_driver *) git_merge_driver_lookup(const char *name);
 typedef struct git_merge_driver_source git_merge_driver_source;
 
 /** Get the repository that the source data is coming from. */
-GIT_EXTERN(const git_repository *) git_merge_driver_source_repo(
+GIT_EXTERN(git_repository *) git_merge_driver_source_repo(
 	const git_merge_driver_source *src);
 
 /** Gets the ancestor of the file to merge. */

src/merge_driver.c

@@ -32,7 +32,7 @@ static struct merge_driver_registry merge_driver_registry;
 
 static void git_merge_driver_global_shutdown(void);
 
-const git_repository* git_merge_driver_source_repo(const git_merge_driver_source *src)
+git_repository* git_merge_driver_source_repo(const git_merge_driver_source *src)
 {
 	assert(src);
 	return src->repo;