supporting N3 @base

euler --pass http://www.dajobe.org/2004/01/turtle/tests/test-30.ttl

actually gives

@prefix math: <http://www.w3.org/2000/10/swap/math#>.
@prefix p0: <http://example.org/ns2#>.
@prefix nsp0: <http://www.dajobe.org/2004/01/turtle/tests/>.
@prefix e: <http://eulersharp.sourceforge.net/2003/03swap/log-rules#>.
@prefix list: <http://www.w3.org/2000/10/swap/list#>.
@prefix q: <http://www.w3.org/2004/ql#>.
@prefix xsd: <http://www.w3.org/2001/XMLSchema#>.
@prefix log: <http://www.w3.org/2000/10/swap/log#>.
@prefix nsp1: <http://example.org/ns/>.
@prefix r: <http://www.w3.org/2000/10/swap/reason#>.
@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#>.
@prefix fn: <http://www.w3.org/2006/xpath-functions#>.
@prefix time: <http://www.w3.org/2000/10/swap/time#>.
@prefix nsp2: <http://example.org/ns/foo/>.
@prefix : <http://example.org/ns/foo/bar#>.
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix var: <http://localhost/var#>.
@prefix str: <http://www.w3.org/2000/10/swap/string#>.
@prefix owl: <http://www.w3.org/2002/07/owl#>.
@prefix n3: <http://www.w3.org/2004/06/rei#>.

nsp0:a1 nsp0:b1 nsp0:c1.
nsp1:a2 nsp1:b2 nsp1:c2.
nsp2:a3 nsp2:b3 nsp2:c3.
:a4 :b4 :c4.
p0:a5 p0:b5 p0:c5.