clean up msp430 cpu-conf.h
fix main return for msp430

mspgcc handles main specially, this introduces code to make main
behave normally
stack alignment workaround

Should be fixed in thread.c instead, this is just a temporary
workaround to enable msp-430 threads in the mean time.
improve programmer handling in msb-430-common
msp430 lpm stub
add some documentation to lpm.h