fix bugs of softice.ASM, "Execution Timing", and "Guard Pages".

[yotuki]

Thank you for your useful samples. I found the following problems of your samples.

• softice.ASM does not set a exception handler. And, Flat Assembler generates "icebp" from "int1" mnemonic.
• Execution Timing tests calculate "initial - end".
• Guard Pages test does not jump to the allocated pages.

I fixed softice.ASM and Execution Timing tests. And, I reimplemented Guard Pages test using assembly language. If you please, pull my commit.