The next RewriteRule redirects every request to bootstrap.php except the filextenstions between your parentheses

RewriteEngine on    
RewriteRule !\.(js|ico|gif|jpg|png|css|pdf|doc|txt|htm|html|xml|ttf|flv|swf|xml|ics|htc)$ bootstrap.php

Can you really exclude ALL files witouth proclaiming them like above?

So that all demands should redirect to boostrap.php when the request isn't a file

Perhaps you should look into the file whether is available and it is a normal file.

RewriteEngine on
RewriteCond %{REQUEST_FILENAME}       !-f
RewriteRule ^(.*) bootstrap.php [L]

Maybe with this, every file with 4 letter extension wouldn't mind to bootstrap.php

RewriteEngine on    
RewriteRule !\.[\d]{4}$ bootstrap.php