Description:
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some timestamps returns a negative value but should return false according to the 
valid formats.

Test script:
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<?php

// valid timestamp for 2011-10-26
var_dump(strtotime(1319580000)); // returns int(-62143152563) 
                                 // but should return false



Expected result:
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bool(false)

Actual result:
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int(-62143152563)