errors: use lowercase

Use lowercase for our error messages, per our custom.

src/streams/socket.c

@@ -138,7 +138,7 @@ static ssize_t socket_write(git_stream *stream, const char *data, size_t len, in
 	errno = 0;
 
 	if ((written = p_send(st->s, data, len, flags)) < 0) {
-		net_set_error("Error sending data");
+		net_set_error("error sending data");
 		return -1;
 	}
 
@@ -151,7 +151,7 @@ static ssize_t socket_read(git_stream *stream, void *data, size_t len)
 	git_socket_stream *st = (git_socket_stream *) stream;
 
 	if ((ret = p_recv(st->s, data, len, 0)) < 0)
-		net_set_error("Error receiving socket data");
+		net_set_error("error receiving socket data");
 
 	return ret;
 }

src/transports/auth_negotiate.c

@@ -144,7 +144,7 @@ static int negotiate_next_token(
 		&output_token,
 		NULL,
 		NULL))) {
-		negotiate_err_set(status_major, status_minor, "Negotiate failure");
+		negotiate_err_set(status_major, status_minor, "negotiate failure");
 		error = -1;
 		goto done;
 	}

src/worktree.c

@@ -238,21 +238,21 @@ int git_worktree_validate(const git_worktree *wt)
 
 	if (!is_worktree_dir(wt->gitdir_path)) {
 		git_error_set(GIT_ERROR_WORKTREE,
-			"Worktree gitdir ('%s') is not valid",
+			"worktree gitdir ('%s') is not valid",
 			wt->gitlink_path);
 		return GIT_ERROR;
 	}
 
 	if (wt->parent_path && !git_path_exists(wt->parent_path)) {
 		git_error_set(GIT_ERROR_WORKTREE,
-			"Worktree parent directory ('%s') does not exist ",
+			"worktree parent directory ('%s') does not exist ",
 			wt->parent_path);
 		return GIT_ERROR;
 	}
 
 	if (!git_path_exists(wt->commondir_path)) {
 		git_error_set(GIT_ERROR_WORKTREE,
-			"Worktree common directory ('%s') does not exist ",
+			"worktree common directory ('%s') does not exist ",
 			wt->commondir_path);
 		return GIT_ERROR;
 	}
@@ -517,7 +517,7 @@ int git_worktree_is_prunable(git_worktree *wt,
 	{
 		if (!reason.size)
 			git_buf_attach_notowned(&reason, "no reason given", 15);
-		git_error_set(GIT_ERROR_WORKTREE, "Not pruning locked working tree: '%s'", reason.ptr);
+		git_error_set(GIT_ERROR_WORKTREE, "not pruning locked working tree: '%s'", reason.ptr);
 		git_buf_dispose(&reason);
 
 		return 0;
@@ -526,7 +526,7 @@ int git_worktree_is_prunable(git_worktree *wt,
 	if ((popts.flags & GIT_WORKTREE_PRUNE_VALID) == 0 &&
 		git_worktree_validate(wt) == 0)
 	{
-		git_error_set(GIT_ERROR_WORKTREE, "Not pruning valid working tree");
+		git_error_set(GIT_ERROR_WORKTREE, "not pruning valid working tree");
 		return 0;
 	}
 
@@ -558,7 +558,7 @@ int git_worktree_prune(git_worktree *wt,
 		goto out;
 	if (!git_path_exists(path.ptr))
 	{
-		git_error_set(GIT_ERROR_WORKTREE, "Worktree gitdir '%s' does not exist", path.ptr);
+		git_error_set(GIT_ERROR_WORKTREE, "worktree gitdir '%s' does not exist", path.ptr);
 		err = -1;
 		goto out;
 	}
@@ -578,7 +578,7 @@ int git_worktree_prune(git_worktree *wt,
 	git_buf_attach(&path, wtpath, 0);
 	if (!git_path_exists(path.ptr))
 	{
-		git_error_set(GIT_ERROR_WORKTREE, "Working tree '%s' does not exist", path.ptr);
+		git_error_set(GIT_ERROR_WORKTREE, "working tree '%s' does not exist", path.ptr);
 		err = -1;
 		goto out;
 	}