Implement Mario's suggestions:
- Clean up code replace merge algorithm with a function.
- Fix for_statement setting control variable to not a constant.
- Fix for_statement checking BY expression to get correct value for optimization
branch.

Thanks Mario.

		IEC 61131-3 Annex F	Examples (informative)

This directory contains example code take from:

Annex F of Draft 2nd edition of the IEC 61131-3 standard (1998)
"PROGRAMMABLE CONTROLLERS - PROGRAMMING LANGUAGES"