Previously, these were not implemented, and Object#== and #eql?
were used.  This tries to check the proc internals to make sure
that procs created from separate blocks are treated as not equal,
but procs created from the same block are treated as equal, even
when the lazy proc allocation optimization is used.

Implements [Feature #14267]

Now Proc#to_s returns
"#<Proc:0x00000237a0f5f170@t.rb:1>".
However, it is convenient to select a file name by (double-)clicking
on some terminals by separating ' ' instead of '@' like
"#<Proc:0x00000237a0f5f170 t.rb:1>"
[Feature #16101]