FSDB test fixtures with same-time glitches: vcd2fsdb drops them

To test 'value at t = last change at t' logic on an FSDB reader, you need a file with several value changes at one timestamp. vcd2fsdb collapses same-time changes even with -seq_num, so a hand-written VCD does not work. Write the fixture with the FsdbWriter API (ffw_Open, ffw_CreateVarByHandle, ffw_CreateXCoorByHnL, ffw_CreateVarValueByHandle) after raising the glitch count with ffw_SetGlitchNum. In my tests, the reader's GotoXTag under a [t,t] view window already landed on the last of the same-time changes.