Resolve Wrestrict warnings on GCC 8.1.1 (#51)

* Fix several misleading indentation warnings on GCC 8.1.1

* Fix reliance on undefined strcpy/sprintf behavior (-Wrestrict warnings)

The standard states that strcpy results in undefined behavior when the source
and destination buffers overlap. I resolved this with a combination of memmove
and strlen. Note that the resulting code is slightly less efficient.

Similarly, sprintf's behavior is undefined when copying takes place between
objects that overlap. I replaced most of these with a simple strcat, though
one required a temp buffer.

* Fix format in improved-edit.c to match surrounding code

src/improved-edit.c

@@ -358,7 +358,9 @@ void parse_edit_action(int command, char *string, struct descriptor_data *d)
 	s++;
 	temp = *s;
 	*s = '\0';
-	sprintf(buf, "%s%4d: ", buf, (i - 1));
+	char buf3[8];
+	sprintf(buf3, "%4d: ", (i - 1));
+	strcat(buf, buf3);
 	strcat(buf, t);
 	*s = temp;
 	t = s;