Execve reworked for two-pass method. It saves two pages per process,
and makes the stack address the same for all processes.
Variable stack base caused a crash in the shell.
ARG_MAX decreased tp 4096 bytes - max size of argv[] and environ[].
Fixed bug in execve().
UART speed fixed: baud generator runs at half CPU clock rate.
Physio ported from NetBSD 1.0.
Pic32 kernel configuration: option KTRACE disabled, HZ reduced to 20.
Max text/data/stack sizes reduced to 4Mbytes - enough for microcontroller.
Terminate a process on any address error or protection violation.