Description:
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When regenerating session ID with session_regenerate_id() the file with old ID is kept in the appropriate directory. 

Say that I create a session with session_start() and get ID=abcd. Then sess_abcd is created.

Later I decide to generate a different ID for whatever reason, call session_regenerate_id() and get ID=1234. The old file sess_abcd, although truncated, is still kept in the filesystem. IMO it should be removed at the time of session_regenerate_id() completion.

Reproduce code:
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<?
session_start();
echo "session1 = ".session_id();
session_regenerate_id();
echo "session2 = ".session_id();
?>

Expected result:
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Only a single file sess_<session2> should be in session dir.

Actual result:
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However both files are still there...