db_purge bugs in zlib support

[stream1972]

There are two bugs in db_purge zlib support code:

1. Wrong archive streams flushed (copy-paste programming...)
2. Z_FULL_FLUSH must not be used as it clears compression dictionary, this ruins compression. Use Z_SYNC_FLUSH instead.
   The diff below fixed these issues.

diff --git a/sched/db_purge.cpp b/sched/db_purge.cpp
--- a/sched/db_purge.cpp
+++ b/sched/db_purge.cpp
@@ -504,7 +508,7 @@ int archive_result_gz (DB_RESULT& result) {
         fail("ERROR: writing result archive failed\n");
     }
 
-    n = gzflush((gzFile)re_stream, Z_FULL_FLUSH);
+    n = gzflush((gzFile)re_stream, Z_SYNC_FLUSH);
     if (n != Z_OK) {
         fail("ERROR: writing result archive failed (flush)\n");
     }
@@ -538,7 +542,7 @@ int archive_wu_gz (DB_WORKUNIT& wu) {
         fail("ERROR: writing workunit archive failed\n");
     }
 
-    n = gzflush((gzFile)re_stream,Z_FULL_FLUSH);
+    n = gzflush((gzFile)wu_stream,Z_SYNC_FLUSH);
     if (n != Z_OK) {
         fail("ERROR: writing workunit archive failed (flush)\n");
     }
@@ -551,7 +555,7 @@ int archive_wu_gz (DB_WORKUNIT& wu) {
         fail("ERROR: writing workunit index failed\n");
     }
 
-    n = gzflush((gzFile)re_stream,Z_SYNC_FLUSH);
+    n = gzflush((gzFile)wu_index_stream,Z_SYNC_FLUSH);
     if (n != Z_OK) {
         fail("ERROR: writing workunit index failed (flush)\n");
     }

[AenBleidd]

@stream1972, could you please create pull request with your fixes? If no - just let me know and I'll do this by myself

[stream1972]

@AenBleidd Please be so kind and create pull request yourself. My own working tree is a mess from different patches and cherrypicks of different ages.