Check if mod_rewrite is installed before trying to use it

stops those apache 500 errors when it's not installed

htaccess.sample

@@ -1,3 +1,4 @@
+<IfModule mod_rewrite.c>
   RewriteEngine On
 
   # NOTE: change this to your actual Laconica path; may be "/".
@@ -7,6 +8,7 @@ RewriteBase /mublog/
   RewriteCond %{REQUEST_FILENAME} !-f
   RewriteCond %{REQUEST_FILENAME} !-d
   RewriteRule (.*) index.php?p=$1 [L,QSA]
+</IfModule>
 
 <FilesMatch "\.(ini)">
   Order allow,deny