patch 8.0.0793: using wrong terminal name for terminal window

Problem:    Using wrong terminal name for terminal window.
Solution:   When 'term' starts with "xterm" use it for $TERM in a terminal
            window.

src/os_unix.c

@@ -5276,7 +5276,8 @@ mch_job_start(char **argv, job_T *job, jobopt_T *options)
 	    set_child_environment(
 		    (long)options->jo_term_rows,
 		    (long)options->jo_term_cols,
-		    "xterm");
+		    STRNCMP(T_NAME, "xterm", 5) == 0
+						   ? (char *)T_NAME : "xterm");
 	else
 # endif
 	    set_default_child_environment();

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    793,
 /**/
     792,
 /**/