#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.