Get rid of realpath?

[fingolfin]

The realpath executable works well, but it creates a chicken and egg problem: In order to use it, scripts need to locate it. But I think we can rewrite scripts to work without it. Consider this shell script:

#!/bin/sh
LINK="$@"
while [ "$LINK" ]; do
  cd "$(dirname $LINK)"
  LINK="$(readlink $(basename $LINK))"
done
echo "$PWD"

This takes a file path as argument, and returns the "real" path of its parent dir (not quite "real", because it doesn't expand symlinks up to the top, but that shouldn't matter for our purposes).

For example, in gap.sh, right now we have

GAP_DIR="$(cd "$(dirname "$(realpath "$0")")"/.. && pwd)

which could be replaced by

OLDDIR="$PWD"
LINK="$0"
while [ "$LINK" ]; do
  cd "$(dirname $LINK)"
  LINK="$(readlink $(basename $LINK))"
done
cd ..
GAP_DIR="$PWD"
cd "$OLDDIR"

[fingolfin]

Done in 24e0d7657e36318bb9fb2b2509727f80b3492888