#623 Make backtick evaluation more verbose

[bluehazzard]

Give backtick evaluation error handling:
checking return value of wxExecute and report it in some log
add an error stream output into some log

Output the evaluation at the beginning of the build log
* make it user configurable

[Teodor Petrov]

I think this is partially fixed by [r12463 ] If you need something more please reopen.