Fix missing element in external ints for stm32

- stm32, stm32f2 & stm32f4 were missing EXTI_Line11 in external
  interrupts source list, causing out of bounds & interrupt source
  identification
Make LuaRPC funcname long enough for null termination
missing return on stm32[f4] enc handler set functions
prevent calling tmr_int_handler with negative numbers since id indexes into an array
Make sure we actually get a file descriptor before creating new WOFS file
remove unused variable from bit library