closed #2388: Creating a default texture for CCSprite if setTexture(nullptr) is invoked.
Add append function for String class.

The append function is useful when adding a string.
So, I added it to String class.
issue #2388: Checking whether the texture exists.
issue #2388: One more static_cast.
issue #2388: Updating comments for cc_2x2_white_image variable.
issue #2388: Fixing a bug in FadeIn::clone.
Merge pull request #3114 from dumganhar/iss2388-default-texture

closed #2388: Creating a default texture for CCSprite if setTexture(nullptr) is invoked.
Support Tizen 2.2 SDK.
- Update project files.
- based on develop branch.
- HelloCpp, SimpleGame, HelloLua, TestLua available to build.
issue #2300: A fix of missing invoking 'initXXX' in clone method.(FadeOut, DelayTime).
'tile' --> 'getTile', 'orignalTile' --> 'getOrignalTile'
Merge pull request #3123 from pyrasis/tizen_2.2

Support Tizen 2.2 SDK
closed issue #2386 : Fix bug : add a new method to clear the stencil buffer bit used by ClippingNode
Update .travis.yml
Merge pull request #3124 from dumganhar/rename-method

issue #2300: A fix of missing invoking 'initXXX' in clone method.(FadeOut, DelayTime).
Merge pull request #3125 from dabingnn/Iss2386-ClippingNode-AsChild-Bug

closed issue #2386 : ClippingNode works wrongly when being set as a child
Merge pull request #3121 from tks2shimizu/develop

Add append function for String class.
[ci skip]