Bug #61660 bin2hex(hex2bin($data)) != $data

[srgoogleguy]

This bug fix now introduces a second optional argument to hex2bin that will comply with BC.
Additionally, the patch prevents an empty string from being accepted (as the existing patch did not).

[srgoogleguy]

As per our conversation on IRC:

"Just to clarify beforehand, as there is some confusion about this:
hex2bin does not convert a hex number to a binary number. hex2bin converts a hexadecimally encoded binary string into a non-encoded binary string. To emphasize again: hex2bin has (nearly) nothing to do with numbers. It's a way to encode strings (or better to say binary strings, but in PHP all strings are binary). And as every byte of data is encoded using two hexadecimal characters (16 * 16 = 256) the encoded string can't be of odd length. Two hex digits always form a pair."

It's clear that many people agree the documentation on hex2bin is quite confusing in this matter. A note has been made to fix this in the doc. Closing PR...thanks