patch 8.1.1610: there is no way to add or load a buffer without side effects

Problem:    There is no way to add or load a buffer without side effects.
Solution:   Add the bufadd() and bufload() functions.
diff --git a/src/evalfunc.c b/src/evalfunc.c
index b24f55b..954ea9f 100644
--- a/src/evalfunc.c
+++ b/src/evalfunc.c
@@ -71,8 +71,10 @@
 #endif
 static void f_browse(typval_T *argvars, typval_T *rettv);
 static void f_browsedir(typval_T *argvars, typval_T *rettv);
+static void f_bufadd(typval_T *argvars, typval_T *rettv);
 static void f_bufexists(typval_T *argvars, typval_T *rettv);
 static void f_buflisted(typval_T *argvars, typval_T *rettv);
+static void f_bufload(typval_T *argvars, typval_T *rettv);
 static void f_bufloaded(typval_T *argvars, typval_T *rettv);
 static void f_bufname(typval_T *argvars, typval_T *rettv);
 static void f_bufnr(typval_T *argvars, typval_T *rettv);
@@ -526,11 +528,13 @@
 #endif
     {"browse",		4, 4, f_browse},
     {"browsedir",	2, 2, f_browsedir},
+    {"bufadd",		1, 1, f_bufadd},
     {"bufexists",	1, 1, f_bufexists},
     {"buffer_exists",	1, 1, f_bufexists},	/* obsolete */
     {"buffer_name",	1, 1, f_bufname},	/* obsolete */
     {"buffer_number",	1, 1, f_bufnr},		/* obsolete */
     {"buflisted",	1, 1, f_buflisted},
+    {"bufload",		1, 1, f_bufload},
     {"bufloaded",	1, 1, f_bufloaded},
     {"bufname",		1, 1, f_bufname},
     {"bufnr",		1, 2, f_bufnr},
@@ -1920,6 +1924,15 @@
 }
 
 /*
+ * "bufadd(expr)" function
+ */
+    static void
+f_bufadd(typval_T *argvars, typval_T *rettv)
+{
+    rettv->vval.v_number = buflist_add(tv_get_string(&argvars[0]), 0);
+}
+
+/*
  * "bufexists(expr)" function
  */
     static void
@@ -1941,6 +1954,25 @@
 }
 
 /*
+ * "bufload(expr)" function
+ */
+    static void
+f_bufload(typval_T *argvars, typval_T *rettv UNUSED)
+{
+    buf_T	*buf = get_buf_arg(&argvars[0]);
+
+    if (buf != NULL && buf->b_ml.ml_mfp == NULL)
+    {
+	aco_save_T	aco;
+
+	aucmd_prepbuf(&aco, buf);
+	swap_exists_action = SEA_NONE;
+	open_buffer(FALSE, NULL, 0);
+	aucmd_restbuf(&aco);
+    }
+}
+
+/*
  * "bufloaded(expr)" function
  */
     static void