add to test that they indeed trap in user space
thanks to pablogventura@gmail.com and nwolovick@gmail.com

 for f in *.{h,c}; do sed -i .sed 's/[[:blank:]]*$//' $f; done
(Thanks to Nicolás Wolovick)

that is a multiple of the sector size.

however, processes still modify their own p->* without locking

* use xchg only for its atomicness.
* use __sync_synchronize() for both CPU and compiler barrier.

fix Regehr complaint

Use cons.lock for everything.  This eliminates the possibility that two CPUS
independently, simultaneously manipulate the CRTC in cgaputc.

Fix comments

Update URL for 2014

- move log into metadata part of disk, so that marking
that the log's blocks are in use falls out for free
- superblock describes the whole disk (sizes and offets)
- sizes and offsets are computed in one place (mkfs) and
the rest of the code refers to the superblock for these values,
instead of recomputing them.

instead of 1.   ideintr() should wait for nsector_per_block interrupts before
waking up the reader; now it wakes up the reader after 1 interrupt, which
apparently means that the first sector is available of the command instead of all.
For now keep BSIZE to 512.