Store axis as MultiLinestring MultiLinestrings could already be imported but we stored them as multiple Linestrings with identical attributes and even stored Linestrings with self-intersections as multiple single Linestrings with identical attributes. Avoid both by storing as MultiLinestring. In passing, removed unnecessary processing steps in the INSERT statemet for the sys_admin case and ensured that attempts to convert to valid simple features are made after transformation, which might lead to invalid features. Since isrsrange_axis() relies on single Linestrings for linear referencing, add an extra ST_Dump().

--- a/schema/gemma_tests.sql	Wed Mar 11 15:54:37 2020 +0100
+++ b/schema/gemma_tests.sql	Wed Mar 11 17:11:23 2020 +0100
@@ -26,8 +26,8 @@
 
 SELECT throws_ok($$
     INSERT INTO waterway.waterway_axis (wtwaxs, objnam) VALUES
-        (ST_GeogFromText('LINESTRING(0 0, 1 1)'), 'test'),
-        (ST_GeogFromText('LINESTRING(0 0, 1 1)'), 'test')
+        (ST_GeogFromText('MULTILINESTRING((0 0, 1 1))'), 'test'),
+        (ST_GeogFromText('MULTILINESTRING((0 0, 1 1))'), 'test')
     $$,
     23505, NULL,
     'No duplicate geometries can be inserted into waterway_axis');