Bug fix and enhancement against InfiniteSlideShow

!'ve been trying to integrate InfiniteSlideShow with my project, and resolved some issues as follows:

1) Xcode 6.x complains of SDWebImage compiling errors.
- Updating SDWebImage from 3.5.4 to 3.7.1 can resolve above errors.

2) Syntax mistakes in InfiniteSlideShow.m cause animation duration always equal with 1.0f.
- Commit efc4e82 intends to fix this.

3) Bug fix: fix crash when dataSource is empty
- See commit feb71d6

4) Add support for reloading slideshow images.