MB-13715 Compare skipped common prefix in HB+trie iterator
MB-13715 Compare skipped common prefix in HB+trie iterator

- If chunks in skipped common prefix among keys differs to those
in 'start key' passed to HB+trie iterator initialization function,
incorrect key can be returned.

- Added routines that compare those skipped prefixes in both HB+trie's
prev() and next() functions.

Change-Id: I25fd0d0d36b761c7a0c26727411fadbb53f646d7

joliss/forestdb,nvoron23/forestdb,zhaog/forestdb,yyangpan/forestdb,couchbase/forestdb,couchbase/forestdb,jinxuan/forestdb,wurikiji/forestdb,nvoron23/forestdb,jinxuan/forestdb,wurikiji/forestdb,hisundar/forestdb,sushmaad/forestdb,zhaog/forestdb,hisundar/forestdb,seem-sky/forestdb,yyangpan/forestdb,joliss/forestdb,sushmaad/forestdb,seem-sky/forestdb