x86: Move address environment switch from the task switchers to the interrupt handler.  That may save doing the action multiple times per interrupt

SH: Move address environment switch from the task switchers to the interrupt handler.  That may save doing the action multiple times per interrupt

MIPS: Move address environment switch from the task switchers to the interrupt handler.  That may save doing the action multiple times per interrupt

AVR32: Move address environment switch from the task switchers to the interrupt handler.  That may save doing the action multiple times per interrupt

AVR32: Move address environment switch from the task switchers to the interrupt handler.  That may save doing the actin multiple times per interrupt

ARM: Move address environment switch from the task switchers to the interrupt handler.  That may save doing the actin multiple times per interrupt

ARM: Move address environment switch from the task switchers to the interrupt handler.  That may save doing the actin multiple times per interrupt

Rename up_addrenv_assign() to up_addrenv_clone() and generalize its arguments so that can be used for other purposes

Fix confusion about what is a page of data and what is a page of L2 page table; restructure functions to reduce duplicated logic

addrenv interface changes: up_addrenv_create() may need to create .text and .bss/.data separately because of differing access privileges (read/execute vs read/write).  And, as a consequence, up_addrenv_vaddr() needs to be split into up_addrenv_vtext(0 and up_addrenv_vdata().

Add addrenv.h; First cut at Cortex-A address environment structures; Add configuration options to setup address enviornment

Change CONFIG_ADDRENV to CONFIG_ARCH_ADDRENV; change how it is selected -- the architecure must first declare support

Recent STM32 UART change:  Wasn't that logic backward?  Shouldn't that have been disable the USART if (1) we don't have than many USARTs OR (2) we don't have that particular USART -- not AND.

STM32 F401:  Only 3 USARTS, but need to set STM32_NUSARTS to six because they are not numbered sequentially