definitive fix of issue #76: remove internal overflow of u64 when calculating least common multiple of task intervals.

Test for overflow when translating task periods/intervals to integer variable.

partial fix to issue #76 - calculate task periods with 1ms (instead of 1ns) resolution. Allows for tasks with periods larger than 4.295s, but smaller than 50 days.

partial fix for issue 74: allow deref of REF in left hand side of assignment (only works in FUNCTIONS for now)

fix issue #78: IL NOT operator not working

fix issue#77 - when IL FB followed by SFC FB, non-existant error was detected in IL code.

revert commits improved performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR)

Following commits are reverted:
mjsousa 0b275a2 improve performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR) -- increase hardcoded limit to 499
mjsousa 2228799 improve performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR) -- Add comments!!
mjsousa ce81fa6 improve performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR)"

The reason is that they cause regression in some cases (if function is
used as argument for function block, for example) and this is not
fixed for a long time.

merge

fix backup/restore functions: now also backup/restore programs instantiated to run inside tasks.

add include <time.h>, required for time_t

improve performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR) -- increase hardcoded limit to 499

improve performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR) -- Add comments!!

improve performance of some extensible Standard Functions (ADD, MUL, AND, OR, XOR)"

Fix method ./configure uses to determine bison version (did not work in bourne shell) (submitted by anonymous)"

fix bug: allow variables with names starting with 'var' to be used in the first line of POU body

Abort compilation when finding R_EDGE or F_EDGE

Fix bug: XOR operator was broken for ANY_BIT types. No XOR__[DL]WORD__[DL]WORD functions were generated.

Add some comments to code regarding backup/restore functions

fix initialization of variable (was not following ISO C++ rules)

make generating backup/restore functions a command line option (off by default).

add support for generating functions to backup/restore the internal state of the PLC.

delete unused variable.

handle POUs with no VAR .. END_VAR blocks

fix bug introduced in previous commit (matiec was unable to parse SFC code)

Fix tracking of line numbers in IL code (error messages were previously indicating incorrect line number).

Fix bug in datatype narrowing algorithm affecting IL code.

Set the symbol->token member in symbolic_variables_c objects.

Debugging helper class: print value of tokens in debugging output.

Fix bug: allow global variables of type DT (initial values for DT are not const!)

Add comment stating how to enable debug option in flex.