[swedish] Improve handling of -öst

Change -öst to -ös when preceded by any of 'iklnprtuv' rather than
just 'l'.

The new rule only requires the -öst to be in R1 whereas previously
we required all of -löst to be.  This second tweak doesn't seem to
affect any words ending -löst but it conflates a few extra cases
when combined with the expanded list of preceding letters, and seems
more logical linguistically (since -ös is akin to -ous in English).

Fixes #152, reported by znakeeye.

algorithms/swedish.sbl

@@ -9,7 +9,7 @@ externals ( stem )
 
 integers ( p1 x )
 
-groupings ( v s_ending )
+groupings ( v s_ending ost_ending )
 
 stringescapes {}
 
@@ -23,6 +23,8 @@ define v 'aeiouy{a"}{ao}{o"}'
 
 define s_ending  'bcdfghjklmnoprtvy'
 
+define ost_ending 'iklnprtuv'
+
 define mark_regions as (
 
     $p1 = limit
@@ -52,10 +54,11 @@ backwardmode (
         and ([next] delete)
     )
 
-    define other_suffix as setlimit tomark p1 for (
-        [substring] among(
+    define other_suffix as (
+        setlimit tomark p1 for ([substring])
+        among(
             'lig' 'ig' 'els' (delete)
-            'l{o"}st'        (<-'l{o"}s')
+            '{o"}st'         (ost_ending <-'{o"}s')
             'fullt'          (<-'full')
         )
     )