[1818] Prepend to PYTHONPATH, don't replace it

tests/lettuce/setup_intree_bind10.sh.in

@@ -23,7 +23,7 @@ BIND10_PATH=@abs_top_builddir@/src/bin/bind10
 PATH=@abs_top_builddir@/src/bin/bind10:@abs_top_builddir@/src/bin/bindctl:@abs_top_builddir@/src/bin/msgq:@abs_top_builddir@/src/bin/auth:@abs_top_builddir@/src/bin/resolver:@abs_top_builddir@/src/bin/cfgmgr:@abs_top_builddir@/src/bin/cmdctl:@abs_top_builddir@/src/bin/stats:@abs_top_builddir@/src/bin/xfrin:@abs_top_builddir@/src/bin/xfrout:@abs_top_builddir@/src/bin/zonemgr:@abs_top_builddir@/src/bin/ddns:@abs_top_builddir@/src/bin/dhcp6:@abs_top_builddir@/src/bin/sockcreator:$PATH
 export PATH
 
-PYTHONPATH=@abs_top_builddir@/src/bin:@abs_top_builddir@/src/lib/python/isc/log_messages:@abs_top_builddir@/src/lib/python:@abs_top_builddir@/src/lib/dns/python/.libs:@abs_top_builddir@/src/lib/xfr/.libs:@abs_top_builddir@/src/lib/log/.libs:@abs_top_builddir@/src/lib/util/io/.libs:@abs_top_builddir@/src/lib/python/isc/config:@abs_top_builddir@/src/lib/python/isc/acl/.libs:@abs_top_builddir@/src/lib/python/isc/datasrc/.libs
+PYTHONPATH=@abs_top_builddir@/src/bin:@abs_top_builddir@/src/lib/python/isc/log_messages:@abs_top_builddir@/src/lib/python:@abs_top_builddir@/src/lib/dns/python/.libs:@abs_top_builddir@/src/lib/xfr/.libs:@abs_top_builddir@/src/lib/log/.libs:@abs_top_builddir@/src/lib/util/io/.libs:@abs_top_builddir@/src/lib/python/isc/config:@abs_top_builddir@/src/lib/python/isc/acl/.libs:@abs_top_builddir@/src/lib/python/isc/datasrc/.libs:$PYTHONPATH
 export PYTHONPATH
 
 # If necessary (rare cases), explicitly specify paths to dynamic libraries