Functions that are in declared twice in the doc pages are not handled

[moufmouf]

To be handled in special cases:

• json_decode (it returns null on error)
• all functions that are in double (in the PHPDoc, some functions are declared twice with different syntaxes. We can't easily cope with those manually)

[shish]

Cleaning out years-old issues -- if this is still a case that needs handling, some specific examples of functions that need special cases (and don't have them already) would be useful :)