revset: use '%' as an operator for 'only' With this patch, we can make it much easier to specify 'only(A,B)' -> A%B. Similarly, 'only(A)' -> A%. On Windows, '%' is a semi-reserved symbol in the following way: using non-bash shells (e.g. cmd.exe but NOT PowerShell, ConEmu, and cmder), %var% is only expanded when 'var' exists and is surrounded by '%'. That only leaves batch scripts which could prove to be problematic. I posit that this isn't a big issue because any developer of batch scripts already knows that to use '%' one needs to escape it by using a double '%%'. Alternatives to '%' could be '=' but that might be limiting our future if we ever decide to use temporary assignments in a revset.