hi!

i'm sending the first two patches, corresponding to the files i've
checked and corrected from forsyth's set.

i'll submit them as i finish them, so i can get more eyes to spot
errors asap.

credit should go to forsyth.  the first file (0intro) is all his and
the second (allocb) also mostly so.  i corrected the Block struct and
added BALLOC, blockalloclen and readblist, in addition to finding out
that most of these functions are actually at /sys/src/9/port/qio.c .


-rodri