rename(): Correct more issues.  (1) Move to the root directory in the pseudo file system, (2) Fix path naming calculation when the path is the root directory of a mounted file system, and (3) dont't do the rename if the source and destination of the rename are the same.

Add logic to VFS rename:  If target of rename exists and is a directory, then the source file should be moved 'under' the target directory.  POSIX also requires that if the target is a file, then that old file must be deleted.

Minor typos

Approved-by: Gregory Nutt

Apparently setvbuf() size can be nonzero with _IONBF.  That makes no sense, but is necessary if setbuf() is to work as it is defined at OpenGroup.org.

Merged in david_s5/nuttx-6/david_s5/typo-up_exitc-edited-online-with-bitbuck-1486672675169 (pull request #207)

Typo up_exit.c edited online with Bitbucket

Approved-by: Gregory Nutt

STM32 & STM32F7 Fixes the bkp reference counter issue

Approved-by: Gregory Nutt

  Allow for complete MCG_C2 definition from the boart.h file
  Moved #ifdef out of code by setting default values for
  Allow for individule bit setting in MCG_C2 for
    BOARD_EXTCLOCK_MCG_C2
    BOARD_MCG_C2_FCFTRIM
    BOARD_MCG_C2_LOCRE0
  Added range and sanity checking

  Added BOARD_MCG_C2_FCFTRIM and BOARD_MCG_C2_LOCRE0 to
  configure the MCG_C2 register
  cleanup of some comments

  Original BOARD_FR_DIV was never used - that is a good thing because
  the value ws definec shifted and the code also shifited it.

  We define the bits as a common set of names. This means that
  an index may be added to a name i.e. LOCK is LOCK0 as that is
  the superset name.