(#5832) - new feature: force update.

* (#5832) - new feature: force update.
add a `force` option to `put` operation to allow update based on
non-leaf revison and generate a new conflict revision, instead of
reporting update conflict error.
it is implemented by generating `new_edits=false` option.

* optimized force update feature with method proposed by @ronag.
need not to fetch `revisions` from db, 2 revisions are enough,
namely the new generated one and the old one provided by the user.

* bugfix:explictly set radix to 10 for parseInt().

* fix an unintented change caused coverage becomes < 100%.

* replace const with var to fix PhantomJS tests failure.

* add test case of force putting on second level parent node.

* a simple note on the new `force` option for put() api.

docs/_includes/api/create_document.html

@@ -7,6 +7,8 @@
 
 Create a new document or update an existing document. If the document already exists, you must specify its revision `_rev`, otherwise a conflict will occur.
 
+If you want to update an existing document even if there's conflict, you should specify the base revision `_rev` and use `force=true` option, then a new conflict revision will be created.
+
 There are some [restrictions on valid property names of the documents](http://wiki.apache.org/couchdb/HTTP_Document_API#Special_Fields). If you try to store non-JSON data (for instance `Date` objects) you may see [inconsistent results](http://pouchdb.com/errors.html#could_not_be_cloned).
 
 #### Example Usage:

tests/integration/test.conflicts.js

@@ -116,6 +116,78 @@ adapters.forEach(function (adapter) {
       });
     });
 
+    it('force put ok on 1st level', function () {
+      var db = new PouchDB(dbs.name);
+      var docId = "docId";
+      var rev1, rev2, rev3, rev2_;
+      // given
+      return db.put({_id: docId, update:1}).then(function (result) {
+        rev1 = result.rev;
+        return db.put({_id: docId, update:2.1, _rev: rev1});
+      }).then(function (result) {
+        rev2 = result.rev;
+        return db.put({_id: docId, update:3, _rev:rev2});
+      })
+      // when
+      .then(function (result) {
+        rev3 = result.rev;
+        return db.put({_id: docId, update:2.2, _rev: rev1}, {force: true});
+      })
+      // then
+      .then(function (result) {
+        rev2_ = result.rev;
+        rev2_.should.not.equal(rev3);
+        rev2_.substring(0, 2).should.equal('2-');
+        should.exist(result.ok, 'update based on nonleaf revision');
+
+        return db.get(docId, {conflicts: true, revs: true});
+      }).then(function (doc) {
+        doc._rev.should.equal(rev3);
+        doc._conflicts.should.eql([rev2_]);
+
+        return db.get(docId, {conflicts: true, revs: true, rev: rev2_});
+      }).then(function (doc) {
+        console.log("the force doc", doc);
+      });
+    });
+
+    it('force put ok on 2nd level', function () {
+      var db = new PouchDB(dbs.name);
+      var docId = "docId";
+      var rev2, rev3, rev4, rev3_;
+      // given
+      return db.put({_id: docId, update: 1}).then(function (result) {
+        return db.put({_id: docId, update: 2, _rev: result.rev});
+      }).then(function (result) {
+        rev2 = result.rev;
+        return db.put({_id: docId, update: 3.1, _rev: rev2});
+      }).then(function (result) {
+        rev3 = result.rev;
+        return db.put({_id: docId, update: 4, _rev: rev3});
+      })
+      // when
+      .then(function (result) {
+        rev4 = result.rev;
+        return db.put({_id: docId, update:3.2, _rev: rev2}, {force: true});
+      })
+      // then
+      .then(function (result) {
+        rev3_ = result.rev;
+        rev3_.should.not.equal(rev4);
+        rev3_.substring(0, 2).should.equal('3-');
+        should.exist(result.ok, 'update based on nonleaf revision');
+
+        return db.get(docId, {conflicts: true, revs: true});
+      }).then(function (doc) {
+        doc._rev.should.equal(rev4);
+        doc._conflicts.should.eql([rev3_]);
+
+        return db.get(docId, {conflicts: true, revs: true, rev: rev3_});
+      }).then(function (doc) {
+        console.log("the force put doc", doc);
+      });
+    });
+
     // Each revision includes a list of previous revisions. The
     // revision with the longest revision history list becomes the
     // winning revision. If they are the same, the _rev values are