Output error messages for command line includes

The code that adds an include path to the array of paths doesn't check
the lenght of the path (which can cause overflows because of strcpy).

It doesn't check if the max number of paths has been reached, either.

This patch adds error messages for such cases, giving the user more
information than before and crashing the assembly instead of
continuing and failing when it can't find a file to include.

src/asm/fstack.c

@@ -179,6 +179,16 @@ fstk_Dump(void)
 void 
 fstk_AddIncludePath(char *s)
 {
+	if (NextIncPath == MAXINCPATHS) {
+		fatalerror("Too many include directories passed from command line");
+		return;
+	}
+
+	if (strlen(s) > _MAX_PATH) {
+		fatalerror("Include path too long '%s'",s);
+		return;
+	}
+
 	strcpy(IncludePaths[NextIncPath++], s);
 }