Work on fetch more
Working fetch more, but settings/tests needs updating
pz:extendrecs number of records in extended mode

If pz:extendrecs is defined it is the maximum number of records
for a target for a show that would otherwise be partial.
Add test using pz:extendrecs
Merge branch 'master' into fetch_more
Refactor: show_range_start deals with extended fetch
Revise extended fetch algorithm

If the show records returned were the last in the sorted "window" of
records per-client , an extended fetch will be attempted. Only if there
are more records to be fetched (hit count depending) and pz:extendrecs
is defined, another fetch will be initiated.
Merge branch 'master' into fetch_more
Change log msg for Pazpart start/stop

Now using same style as Metaproxy, ie
 Pazpar2 start SHA1 / Pazpar2 stop .
Merge branch 'master' into fetch_more
New pz:metadata attribute, empty="empty-value" PAZ-858

With this attribute, Pazpar2 treates an empty pz:metadata type
as having the value for "empty"  - if empty!
Simplify XSLs by using new pz:metadata attribute 'empty'.
test tmarc.xsl same as the official one in etc
Make use of the pz:metadata empty in tests
Fix missing limitmap warning PAZ-859
Use session_log when possible
Update NEWS
Delete traling whitespace from NEWS
Version 1.6.26
Fix text/cdata nodes collection