Fix installpath for docs caused by misuse of automake

This fixes a long standing (personal) mystery in automake. Automake
isn't terribly smart and doesn't strip whitespace at the end of lines.
That means that after evaluating this line:

    wibble = foo bar baz # this is a comment

the value of wibble is "foo bar baz "

*sigh* This was introduced in c6e74d4, which was probably copypasta'd
from God knows where.