examples: fix the warning‎ of 0_usart demo.
examples: fix the warning‎ of 1_kernel_event_basic demo.
examples: fix the warning‎ of 1_kernel_mailbox_basic demo.
examples: fix the warning‎ of 1_kernel_mem_ringbuffer demo.
examples: fix the warning‎ of 1_kernel_message_queue demo.
examples: fix the warning‎ of 1_kernel_mutex_basic demo.
examples: fix the warning‎ of 1_kernel_thread_prioinvert demo.
examples: fix the warning‎ of 2_filesystem_ramfs demo.
examples:fix the error of 2_filesystem_romfs demo.
examples: fix the warning‎ of 2_mtd_nand demo.
drivers:fix the warning‎ of emac driver
examples: fix the warning‎ of 3_networking_ftp_server demo.
examples: fix the warning‎ of 3_networking_nfs demo.
examples: fix the warning‎ of 4_gui_examples demo.
examples: fix the warning‎ of demo_view_digtube.c.
examples: fix the warning‎ of 4_gui_photo_frame demo.
drivers: fix the warning‎ of i2c driver.
drivers: fix the warning‎ of hy27uf081g nand flash driver.
examples: fix the warning‎ of realboard demo.
Merge pull request #28 from nongxiaoming/master

 fix the warning‎ of all the demo.