Error with virtual path in case a physical path is not a part of it.

Hi everyone!
I have problem with routing on my hosting where it is not possible to set "DocumentRoot" to 'public' subfolder (in my project 'index.php' placed in 'public' directory). I was created a '.htaccess' file with content:
```
DirectoryIndex /public/index.php
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule ^(.+) $1 [L]
RewriteCond %{DOCUMENT_ROOT}/public%{REQUEST_URI} -f
RewriteRule ^(.+) /public/$1 [L]
RewriteCond %{DOCUMENT_ROOT}/public/index.php -f
RewriteRule ^(.*) /public/index.php
```
And I see that all my routes was broken in $env['PATH_INFO'].
For example: 'ts' instead '/contacts'.
It happened because on line 143 in 'Slim/Environment.php':
```
$env['PATH_INFO'] = substr_replace($requestUri, '', 0, strlen($physicalPath)); // <-- Remove physical path
```
first seven symbols (strlen('/public')) was removed from $env['PATH_INFO'] but it does not contain '/public'.
And I was added a logic to check if physical path is a really part of $env['PATH_INFO']:
```
if (strpos($requestUri, $physicalPath) === 0) {
    $env['PATH_INFO'] = substr($requestUri, strlen($physicalPath)); // <-- Remove physical path
} else {
    $env['PATH_INFO'] = $requestUri; // <-- Physical path is not a part of request uri
}
```
P.S. Sorry for my bad English. :)