When were the 'and' and 'or' alternative tokens introduced in C++?

To actually answer the question :

They were defined in the first C++ standard.

MSVC supports them as keywords only if you use the /Za option to disable extensions; this is true from at least VC7.1 (VS2003).

You can get them supported as macros by including iso646.h.

My guess is they believe that making them keywords by default would break too much existing code (and I wouldn't be surprised if they are right).

From the first ISO C++ standard C++98, this is described in 2.5/ Alternative tokens [lex.digraph]:

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1. Alternative token representations are provided for some operators and punctuators.
2. In all respects of the language, each alternative token behaves the same, respectively, as its primary token, except for its spelling. The set of alternative tokens is defined in Table 2.

Table 2 - Alternative tokens

    alternative primary | alternative primary | alternative primary
    --------------------+---------------------+--------------------
       <%          {    |    and         &&   |    and_eq      &=
       %>          }    |    bitor       |    |    or_eq       |=
       <:          [    |    or          ||   |    xor_eq      ^=
       :>          ]    |    xor         ^    |    not         !
       %:          #    |    compl       ~    |    not_eq      !=
       %:%:        ##   |    bitand      &    |

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So it's been around since the earliest days of the C++ standardisation process. The reason so few people are aware of it is likely because the main use case was for people operating in environments where the full character set wasn't necessarily available. For example (and this is stretching my memory), the baseline EBCDIC character set on the IBM mainframes did not have the square bracket characters [ and ].