runshell followed by git annex webapp didn't install that stuff, because
GIT_ANNEX_APP_BASE is not set. Running git-annex.linux/git-annex-webapp did
install that stuff, since that script set the env var. I noticed this with
the termux port whose instructions currently go that way.
Seems the right thing to do is to move the env var setting to runshell.
Unless busybox doesn't support readlink -f, then it just uses readlink and
symlinking won't work. Also, OSX has no readlink -f so not done there.
Thanks, jlebar.
