Fix comment parsing in interp_simple.c

loader.rc has comment lines without a trailing space, which get
interpreted as commands. Avoid this by only matching against the
backslash character.

Reviewed by:	imp, tsoome
Differential Revision:	https://reviews.freebsd.org/D20491

stand/common/interp_simple.c

@@ -114,7 +114,7 @@ interp_include(const char *filename)
 		line++;
 		flags = 0;
 		/* Discard comments */
-		if (strncmp(input+strspn(input, " "), "\\ ", 2) == 0)
+		if (strncmp(input+strspn(input, " "), "\\", 1) == 0)
 			continue;
 		cp = input;
 		/* Echo? */