Fix backlashes injected by mysqli escape

I was trying to insert some binary data with null chars and ran into a weird problem, tracked it down to preg_replace requiring backslashes to be doubled if used inside of replacements.
```php
$original = "string\x00with\x00nulls\x00andDollar\\$23";
$replacements = $db->escape($original);
$randomstr = '/MD5VALUE/';
echo "Original PRE-REPLACED value: $original" . PHP_EOL;
echo "Escaped PRE-REPLACED value: $replacements" . PHP_EOL;
$sql = "MD5VALUE";
$replacements = '\'' . preg_replace('/\$([0-9]*)/', '\\\$$1',$replacements) . '\'';
$sql = preg_replace($randomstr, $replacements, $sql,1);
echo 'Currently inserted: ' . $sql .  PHP_EOL;

$sql = "MD5VALUE";
$replacements = '\'' . preg_replace(array('/\\\\/','/\$([0-9]*)/'), array('\\\\\\\\','\\\$$1'), $db->escape($original)) . '\'';
$sql = preg_replace($randomstr, $replacements, $sql, 1);
echo 'Fixed: ' . $sql .  PHP_EOL;
```
Output:
```
Original PRE-REPLACED value: stringwithnullsandDollar\$23
Escaped PRE-REPLACED value: string\0with\0nulls\0andDollar\\$23
Currently inserted: 'stringMD5VALUEwithMD5VALUEnullsMD5VALUEandDollar\$23'
Fixed: 'string\0with\0nulls\0andDollar\\$23'
```
Line 3111 also uses `preg_replace('/\$([0-9]*)/', '\\\$$1',$match[0])` but doesn't escape it with `mysqli_real_escape_string()` so I figured that didn't need to be changed. My problem was with the null char but I'm pretty sure this would have effected other things with backslashes, like \n or \r.
Merge pull request #13 from primeinc/patch-1

Fix backlashes injected by mysqli escape