In @node I/O Callback Example, the example code given doesn't compile. A lot of
it is just inconsistencies with itself, simple mistakes, or using apparently
ancient gpgme functions like init_gpgme (which are fixed in attached patch). One
problem still is the remove_io_cb function: it can't acquire the lock it needs
with the current design of the *tag pointer, and I wasn't sure what the *good*
version of it was supposed to look like.