Add a get_page_length_ function to return current page length for an I/O stream/switch

[Gary Dixon]

Similar to the existing get_line_length_ function, there should be a function that returns current page length of a given I/O switch. The interface would be identical to that of get_line_length_, and is summarized by help -brief output below.

help get_page_length_$(stream switch) -brief

Syntax:
declare get_page_length_$stream entry (char(*), fixed bin(35)) returns (fixed bin);
page_length = get_page_length_$stream (switch_name, code);

Syntax:
declare get_page_length_$switch entry (ptr, fixed bin(35)) returns (fixed bin);
page_length = get_page_length_$switch (switch_ptr, code);

[Eric Swenson]

​https://s3.amazonaws.com/eswenson-multics/public/mcrs/MCR10082.pdf