patch 8.1.0745: compiler warnings for signed/unsigned string

Problem:    Compiler warnings for signed/unsigned string.
Solution:   Remove type casts. (John Marriott)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index 112b67d..6f9f1b9 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -2290,7 +2290,7 @@
 	/* check these explicitly for a more specific error message */
 	if (*ea.arg == '*' || *ea.arg == '+')
 	{
-	    errormsg = (char_u *)_(e_invalidreg);
+	    errormsg = _(e_invalidreg);
 	    goto doend;
 	}
 #endif
diff --git a/src/mbyte.c b/src/mbyte.c
index 9c40072..66a3cc2 100644
--- a/src/mbyte.c
+++ b/src/mbyte.c
@@ -560,7 +560,7 @@
 	else if (GetLastError() == ERROR_INVALID_PARAMETER)
 	{
 codepage_invalid:
-	    return (char_u *)N_("E543: Not a valid codepage");
+	    return N_("E543: Not a valid codepage");
 	}
     }
 #endif
diff --git a/src/version.c b/src/version.c
index 69bbcfc..60d82d2 100644
--- a/src/version.c
+++ b/src/version.c
@@ -796,6 +796,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    745,
+/**/
     744,
 /**/
     743,