working checkpoint.

add comment describing new web server tree.
make room for command line interface.
use new path package to get rid of doubled slashes.
use new Chdir function to avoid goroot + everything.

implement new /pkg/ tree instead of using regexps.

R=gri
DELTA=267  (103 added, 72 deleted, 92 changed)
OCL=27150
CL=27367