Description:
------------
There is a memory leak in pg_escape_bytea() function due to a missing call to PQfreemem().
This issue was first introduced with the following commit:
https://github.com/php/php-src/commit/1ff7c7b9a31bd3242b06436740322f7246a708f0
so all 7.x are affected. 

Test script:
---------------
<?php
define('LN', "\n");

// Big file ~50Mb
$messData = file_get_contents('./bigfile');

for($i=0; $i<3; $i++) {

	$db = pg_connect('host=pgserver port=5432 dbname=testdb user=dbuser password=dbuserpass connect_timeout=5');
	echo "$i Before: ".memStat().LN;
	$escData = pg_escape_bytea($db, $messData);
	echo "$i Esc: ".memStat().LN;
	unset ($escData);
	pg_close($db);
	echo "$i Clear: ".memStat().LN.LN;

}

echo 'End: '.memStat().LN;

sleep (20);


function memStat() {
	return round(memory_get_usage()/1024/1024, 2).' Mb';
}
?>

Actual result:
--------------
Though memory usage reported by memStat() stays the same, the memory usage reported by "top" or "ps" tools will grow.
Also the issue can be reproduced by running the test script with php-fpm and monitoring the OS memory usage.

The patch for this issue should be trivial - one can invoke PQfreemem(to) after
RETVAL_STRINGL(to, to_len-1); /* to_len includes addtional '\0' */ 
in ext/pgsql/pgsql.c or call efree(to) as it being done for pg_unescape_bytea() function.