STM32 PVD: Adds support for STM32's Programmable Voltage Detector feature. I put register access behind CONFIG_STM32_ENERGYLITE as have not checked F1/F2/F4 etc. manuals. Tested on STM32L1. PVD interrupt looks generic, at least #defines it needs are in headers for every chip variant.  By Dmitry Nikolaev, submitted by Juha Niskanen.

Networking: If IPV6 is not enabled, an warning occurs for an unused variable, which is currently used inside the IPV6 block, but declared outside.  From ObitalFox.

sem_wait(): Missing comma on debug statement caused compile error with DEBUG on.  Why hasn't that been noted before?

STM32 RTC counter: Include enable/disable backup domain within critical section.  Per recommendtion of Alexander Oryshchenko.

STM32 F1 RTC Counter:  Now need to enable backup domain write access when setting the time.  From Darcy Gong

Fix an error introduced into stm32_pwr_enablebkp().  That function must preserve the previous state of backup domain access on return.

STM32F429i Disco: (1) Fix a bad return value if the LCD driver is already initialized. (2) The LCD driver initialization is now performed during the early boot sequence.  (3) Increased the size of the message queue from 32 to 64 in the lcd configuration.  From Marco, ocram.lhark@yahoo.com.